Summa Th. I EN Qu.42 a.5
Objection: 1. It would seem that the Son and the Father are not in each other. For the Philosopher (Phys. iv, text. 23) gives eight modes of one thing existing in another, according to none of which is the Son in the Father, or conversely; as is patent to anyone who examines each mode. Therefore the Son and the Father are not in each other.
2. Further, nothing that has come out from another is within. But the Son from eternity came out from the Father, according to Micheas 5:2: "His going forth is from the beginning, from the days of eternity." Therefore the Son is not in the Father.
3. Further, one of two opposites cannot be in the other. But the Son and the Father are relatively opposed. Therefore one cannot be in the other.
On the contrary It is said (Jn 14,10): "I am in the Father, and the Father is in Me."
I answer that There are three points of consideration as regards the Father and the Son; the essence, the relation and the origin; and according to each the Son and the Father are in each other. The Father is in the Son by His essence, forasmuch as the Father is His own essence and communicates His essence to the Son not by any change on His part. Hence it follows that as the Father's essence is in the Son, the Father Himself is in the Son; likewise, since the Son is His own essence, it follows that He Himself is in the Father in Whom is His essence. This is expressed by Hilary (De Trin. v), "The unchangeable God, so to speak, follows His own nature in begetting an unchangeable subsisting God. So we understand the nature of God to subsist in Him, for He is God in God." It is also manifest that as regards the relations, each of two relative opposites is in the concept of the other. Regarding origin also, it is clear that the procession of the intelligible word is not outside the intellect, inasmuch as it remains in the utterer of the word. What also is uttered by the word is therein contained. And the same applies to the Holy Ghost.
Reply to Objection: 1. What is contained in creatures does not sufficiently represent what exists in God; so according to none of the modes enumerated by the Philosopher, are the Son and the Father in each other. The mode the most nearly approaching to the reality is to be found in that whereby something exists in its originating principle, except that the unity of essence between the principle and that which proceeds therefrom is wanting in things created.
2. The Son's going forth from the Father is by mode of the interior procession whereby the word emerges from the heart and remains therein. Hence this going forth in God is only by the distinction of the relations, not by any kind of essential separation.
3. The Father and the Son are relatively opposed, but not essentially; while, as above explained, one relative opposite is in the other.
Objection: 1. It would seem that the Son is not equal to the Father in power. For it is said (Jn 5,19): "The Son cannot do anything of Himself but what He seeth the Father doing." But the Father can act of Himself. Therefore the Father's power is greater than the Son's.
2. Further, greater is the power of him who commands and teaches than of him who obeys and hears. But the Father commands the Son according to Jn 14,31: "As the Father gave Me commandment so do I." The Father also teaches the Son: "The Father loveth the Son, and showeth Him all things that Himself doth" (Jn 5,20). Also, the Son hears: "As I hear, so I judge" (Jn 5,30). Therefore the Father has greater power than the Son.
3. Further, it belongs to the Father's omnipotence to be able to beget a Son equal to Himself. For Augustine says (Contra Maxim. iii, 7), "Were He unable to beget one equal to Himself, where would be the omnipotence of God the Father?" But the Son cannot beget a Son, as proved above (Question , Article ). Therefore the Son cannot do all that belongs to the Father's omnipotence; and hence He is not equal to Him power.
On the contrary It is said (Jn 5,19): "Whatsoever things the Father doth, these the Son also doth in like manner."
I answer that The Son is necessarily equal to the Father in power. Power of action is a consequence of perfection in nature. In creatures, for instance, we see that the more perfect the nature, the greater power is there for action. Now it was shown above (Article ) that the very notion of the divine paternity and filiation requires that the Son should be the Father's equal in greatness---that is, in perfection of nature. Hence it follows that the Son is equal to the Father in power; and the same applies to the Holy Ghost in relation to both.
Reply to Objection: 1. The words, "the Son cannot of Himself do anything," do not withdraw from the Son any power possessed by the Father, since it is immediately added, "Whatsoever things the Father doth, the Son doth in like manner"; but their meaning is to show that the Son derives His power from the Father, of Whom He receives His nature. Hence, Hilary says (De Trin. ix), "The unity of the divine nature implies that the Son so acts of Himself [per se], that He does not act by Himself [a se]."
2. The Father's "showing" and the Son's "hearing" are to be taken in the sense that the Father communicates knowledge to the Son, as He communicates His essence. The command of the Father can be explained in the same sense, as giving Him from eternity knowledge and will to act, by begetting Him. Or, better still, this may be referred to Christ in His human nature.
3. As the same essence is paternity in the Father, and filiation in the Son: so by the same power the Father begets, and the Son is begotten. Hence it is clear that the Son can do whatever the Father can do; yet it does not follow that the Son can beget; for to argue thus would imply transition from substance to relation, for generation signifies a divine relation. So the Son has the same omnipotence as the Father, but with another relation; the Father possessing power as "giving" signified when we say that He is able to beget; while the Son possesses the power of "receiving," signified by saying that He can be begotten.
We next consider the mission of the divine persons, concerning which there are eight points of inquiry:
(1) Whether it is suitable for a divine person to be sent?
(2) Whether mission is eternal, or only temporal?
(3) In what sense a divine person is invisibly sent?
(4) Whether it is fitting that each person be sent?
(5) Whether both the Son and the Holy Ghost are invisibly sent?
(6) To whom the invisible mission is directed?
(7) Of the visible mission
(8) Whether any person sends Himself visibly or invisibly?
Objection: 1. It would seem that a divine person cannot be properly sent. For one who is sent is less than the sender. But one divine person is not less than another. Therefore one person is not sent by another.
2. Further, what is sent is separated from the sender; hence Jerome says, commenting on Ez 16,53: "What is joined and tied in one body cannot be sent." But in the divine persons there is nothing that is separable, as Hilary says (De Trin. vii). Therefore one person is not sent by another.
3. Further, whoever is sent, departs from one place and comes anew into another. But this does not apply to a divine person, Who is everywhere. Therefore it is not suitable for a divine person to be sent.
On the contrary It is said (Jn 8,16): "I am not alone, but I and the Father that sent Me."
I answer that the notion of mission includes two things: the habitude of the one sent to the sender; and that of the one sent to the end whereto he is sent. Anyone being sent implies a certain kind of procession of the one sent from the sender: either according to command, as the master sends the servant; or according to counsel, as an adviser may be said to send the king to battle; or according to origin, as a tree sends forth its flowers. The habitude to the term to which he is sent is also shown, so that in some way he begins to be present there: either because in no way was he present before in the place whereto he is sent, or because he begins to be there in some way in which he was not there hitherto. Thus the mission of a divine person is a fitting thing, as meaning in one way the procession of origin from the sender, and as meaning a new way of existing in another; thus the Son is said to be sent by the Father into the world, inasmuch as He began to exist visibly in the world by taking our nature; whereas "He was" previously "in the world" (Jn 1,1).
Reply to Objection: 1. Mission implies inferiority in the one sent, when it means procession from the sender as principle, by command or counsel; forasmuch as the one commanding is the greater, and the counsellor is the wiser. In God, however, it means only procession of origin, which is according to equality, as explained above (Question , Articles ,6).
2. What is so sent as to begin to exist where previously it did not exist, is locally moved by being sent; hence it is necessarily separated locally from the sender. This, however, has no place in the mission of a divine person; for the divine person sent neither begins to exist where he did not previously exist, nor ceases to exist where He was. Hence such a mission takes place without a separation, having only distinction of origin.
3. This objection rests on the idea of mission according to local motion, which is not in God.
Objection: 1. It would seem that mission can be eternal. For Gregory says (Hom. xxvi, in ), "The Son is sent as He is begotten." But the Son's generation is eternal. Therefore mission is eternal.
2. Further, a thing is changed if it becomes something temporally. But a divine person is not changed. Therefore the mission of a divine person is not temporal, but eternal.
3. Further, mission implies procession. But the procession of the divine persons is eternal. Therefore mission is also eternal.
On the contrary It is said (Ga 4,4): "When the fullness of the time was come, God sent His Son."
I answer that A certain difference is to be observed in all the words that express the origin of the divine persons. For some express only relation to the principle, as "procession" and "going forth." Others express the term of procession together with the relation to the principle. Of these some express the eternal term, as "generation" and "spiration"; for generation is the procession of the divine person into the divine nature, and passive spiration is the procession of the subsisting love. Others express the temporal term with the relation to the principle, as "mission" and "giving." For a thing is sent that it may be in something else, and is given that it may be possessed; but that a divine person be possessed by any creature, or exist in it in a new mode, is temporal.
Hence "mission" and "giving" have only a temporal significance in God; but "generation" and "spiration" are exclusively eternal; whereas "procession" and "giving," in God, have both an eternal and a temporal signification: for the Son may proceed eternally as God; but temporally, by becoming man, according to His visible mission, or likewise by dwelling in man according to His invisible mission.
Reply to Objection: 1. Gregory speaks of the temporal generation of the Son, not from the Father, but from His mother; or it may be taken to mean that He could be sent because eternally begotten.
2. That a divine person may newly exist in anyone, or be possessed by anyone in time, does not come from change of the divine person, but from change in the creature; as God Himself is called Lord temporally by change of the creature.
3. Mission signifies not only procession from the principle, but also determines the temporal term of the procession. Hence mission is only temporal. Or we may say that it includes the eternal procession, with the addition of a temporal effect. For the relation of a divine person to His principle must be eternal. Hence the procession may be called a twin procession, eternal and temporal, not that there is a double relation to the principle, but a double term, temporal and eternal.
Objection: 1. It would seem that the invisible mission of the divine person is not only according to the gift of sanctifying grace. For the sending of a divine person means that He is given. Hence if the divine person is sent only according to the gift of sanctifying grace, the divine person Himself will not be given, but only His gifts; and this is the error of those who say that the Holy Ghost is not given, but that His gifts are given.
2. Further, this preposition, "according to," denotes the habitude of some cause. But the divine person is the cause why the gift of sanctifying grace is possessed, and not conversely, according to Rm 5,5, "the charity of God is poured forth in our hearts by the Holy Ghost, Who is given to us." Therefore it is improperly said that the divine person is sent according to the gift of sanctifying grace.
3. Further, Augustine says (De Trin. iv, 20) that "the Son, when temporally perceived by the mind, is sent." But the Son is known not only by sanctifying grace, but also by gratuitous grace, as by faith and knowledge. Therefore the divine person is not sent only according to the gift of sanctifying grace.
4. Further, Rabanus says that the Holy Ghost was given to the apostles for the working of miracles. This, however, is not a gift of sanctifying grace, but a gratuitous grace. Therefore the divine person is not given only according to the gift of sanctifying grace.
On the contrary Augustine says (De Trin. iii, 4) that "the Holy Ghost proceeds temporally for the creature's sanctification." But mission is a temporal procession. Since then the creature's sanctification is by sanctifying grace, it follows that the mission of the divine person is only by sanctifying grace.
I answer that The divine person is fittingly sent in the sense that He exists newly in any one; and He is given as possessed by anyone; and neither of these is otherwise than by sanctifying grace.
For God is in all things by His essence, power and presence, according to His one common mode, as the cause existing in the effects which participate in His goodness. Above and beyond this common mode, however, there is one special mode belonging to the rational nature wherein God is said to be present as the object known is in the knower, and the beloved in the lover. And since the rational creature by its operation of knowledge and love attains to God Himself, according to this special mode God is said not only to exist in the rational creature but also to dwell therein as in His own temple. So no other effect can be put down as the reason why the divine person is in the rational creature in a new mode, except sanctifying grace. Hence, the divine person is sent, and proceeds temporally only according to sanctifying grace.
Again, we are said to possess only what we can freely use or enjoy: and to have the power of enjoying the divine person can only be according to sanctifying grace. And yet the Holy Ghost is possessed by man, and dwells within him, in the very gift itself of sanctifying grace. Hence the Holy Ghost Himself is given and sent.
Reply to Objection: 1. By the gift of sanctifying grace the rational creature is perfected so that it can freely use not only the created gift itself, but enjoy also the divine person Himself; and so the invisible mission takes place according to the gift of sanctifying grace; and yet the divine person Himself is given.
2. Sanctifying grace disposes the soul to possess the divine person; and this is signified when it is said that the Holy Ghost is given according to the gift of grace. Nevertheless the gift itself of grace is from the Holy Ghost; which is meant by the words, "the charity of God is poured forth in our hearts by the Holy Ghost."
3. Although the Son can be known by us according to other effects, yet neither does He dwell in us, nor is He possessed by us according to those effects.
4. The working of miracles manifests sanctifying grace as also does the gift of prophecy and any other gratuitous graces. Hence gratuitous grace is called the "manifestation of the Spirit" (1Co 12,7). So the Holy Ghost is said to be given to the apostles for the working of miracles, because sanctifying grace was given to them with the outward sign. Were the sign only of sanctifying grace given to them without the grace itself, it would not be simply said that the Holy Ghost was given, except with some qualifying term; just as we read of certain ones receiving the gift of the spirit of prophecy, or of miracles, as having from the Holy Ghost the power of prophesying or of working miracles.
Objection: 1. It would seem that it is fitting also that the Father should be sent. For being sent means that the divine person is given. But the Father gives Himself since He can only be possessed by His giving Himself. Therefore it can be said that the Father sends Himself.
2. Further, the divine person is sent according to the indwelling of grace. But by grace the whole Trinity dwells in us according to Jn 14,23: "We will come to him and make Our abode with him." Therefore each one of the divine persons is sent.
3. Further, whatever belongs to one person, belongs to them all, except the notions and persons. But mission does not signify any person; nor even a notion, since there are only five notions, as stated above (Question , Article ). Therefore every divine person can be sent.
On the contrary Augustine says (De Trin. ii, 3), "The Father alone is never described as being sent."
I answer that The very idea of mission means procession from another, and in God it means procession according to origin, as above expounded. Hence, as the Father is not from another, in no way is it fitting for Him to be sent; but this can only belong to the Son and to the Holy Ghost, to Whom it belongs to be from another.
Reply to Objection: 1. In the sense of "giving" as a free bestowal of something, the Father gives Himself, as freely bestowing Himself to be enjoyed by the creature. But as implying the authority of the giver as regards what is given, "to be given" only applies in God to the Person Who is from another; and the same as regards "being sent."
2. Although the effect of grace is also from the Father, Who dwells in us by grace, just as the Son and the Holy Ghost, still He is not described as being sent, for He is not from another. Thus Augustine says (De Trin. iv, 20) that "The Father, when known by anyone in time, is not said to be sent; for there is no one whence He is, or from whom He proceeds."
3. Mission, meaning procession from the sender, includes the signification of a notion, not of a special notion, but in general; thus "to be from another" is common to two of the notions.
Objection: 1. It would seem that it is not fitting for the Son to be sent invisibly. For invisible mission of the divine person is according to the gift of grace. But all gifts of grace belong to the Holy Ghost, according to 1Co 12,11: "One and the same Spirit worketh all things." Therefore only the Holy Ghost is sent invisibly.
2. Further, the mission of the divine person is according to sanctifying grace. But the gifts belonging to the perfection of the intellect are not gifts of sanctifying grace, since they can be held without the gift of charity, according to 1Co 13,2: "If I should have prophecy, and should know all mysteries, and all knowledge, and if I should have all faith so that I could move mountains, and have not charity, I am nothing." Therefore, since the Son proceeds as the word of the intellect, it seems unfitting for Him to be sent invisibly.
3. Further, the mission of the divine person is a procession, as expounded above (Articles ,4). But the procession of the Son and of the Holy Ghost differ from each other. Therefore they are distinct missions if both are sent; and then one of them would be superfluous, since one would suffice for the creature's sanctification.
On the contrary It is said of divine Wisdom (Sg 9,10): "Send her from heaven to Thy Saints, and from the seat of Thy greatness."
I answer that The whole Trinity dwells in the mind by sanctifying grace, according to Jn 14,23: "We will come to him, and will make Our abode with him." But that a divine person be sent to anyone by invisible grace signifies both that this person dwells in a new way within him and that He has His origin from another. Hence, since both to the Son and to the Holy Ghost it belongs to dwell in the soul by grace, and to be from another, it therefore belongs to both of them to be invisibly sent. As to the Father, though He dwells in us by grace, still it does not belong to Him to be from another, and consequently He is not sent.
Reply to Objection: 1. Although all the gifts, considered as such, are attributed to the Holy Ghost, forasmuch as He is by His nature the first Gift, since He is Love, as stated above (Question , Article ), some gifts nevertheless, by reason of their own particular nature, are appropriated in a certain way to the Son, those, namely, which belong to the intellect, and in respect of which we speak of the mission of the Son. Hence Augustine says (De Trin. iv, 20) that "The Son is sent to anyone invisibly, whenever He is known and perceived by anyone."
2. The soul is made like to God by grace. Hence for a divine person to be sent to anyone by grace, there must needs be a likening of the soul to the divine person Who is sent, by some gift of grace. Because the Holy Ghost is Love, the soul is assimilated to the Holy Ghost by the gift of charity: hence the mission of the Holy Ghost is according to the mode of charity. Whereas the Son is the Word, not any sort of word, but one Who breathes forth Love. Hence Augustine says (De Trin. ix 10): "The Word we speak of is knowledge with love." Thus the Son is sent not in accordance with every and any kind of intellectual perfection, but according to the intellectual illumination, which breaks forth into the affection of love, as is said (Jn 6,45): "Everyone that hath heard from the Father and hath learned, cometh to Me," and (Ps 38,4): "In my meditation a fire shall flame forth." Thus Augustine plainly says (De Trin. iv, 20): "The Son is sent, whenever He is known and perceived by anyone." Now perception implies a certain experimental knowledge; and this is properly called wisdom [sapientia], as it were a sweet knowledge [sapida scientia], according to Si 6,23: "The wisdom of doctrine is according to her name."
3. Since mission implies the origin of the person Who is sent, and His indwelling by grace, as above explained (Article ), if we speak of mission according to origin, in this sense the Son's mission is distinguished from the mission of the Holy Ghost, as generation is distinguished from procession. If we consider mission as regards the effect of grace, in this sense the two missions are united in the root which is grace, but are distinguished in the effects of grace, which consist in the illumination of the intellect and the kindling of the affection. Thus it is manifest that one mission cannot be without the other, because neither takes place without sanctifying grace, nor is one person separated from the other.
Objection: 1. It would seem that the invisible mission is not to all who participate grace. For the Fathers of the Old Testament had their share of grace. Yet to them was made no invisible mission; for it is said (Jn 7,39): "The Spirit was not yet given, because Jesus was not yet glorified." Therefore the invisible mission is not to all partakers in grace.
2. Further, progress in virtue is only by grace. But the invisible mission is not according to progress in virtue; because progress in virtue is continuous, since charity ever increases or decreases; and thus the mission would be continuous. Therefore the invisible mission is not to all who share in grace.
3. Further, Christ and the blessed have fullness of grace. But mission is not to them, for mission implies distance, whereas Christ, as man, and all the blessed are perfectly united to God. Therefore the invisible mission is not to all sharers in grace.
4. Further, the Sacraments of the New Law contain grace, and it is not said that the invisible mission is sent to them. Therefore the invisible mission is not to all that have grace.
On the contrary According to Augustine (De Trin. iii, 4; xv, 27), the invisible mission is for the creature's sanctification. Now every creature that has grace is sanctified. Therefore the invisible mission is to every such creature.
I answer that As above stated (Articles ,4,5), mission in its very meaning implies that he who is sent either begins to exist where he was not before, as occurs to creatures; or begins to exist where he was before, but in a new way, in which sense mission is ascribed to the divine persons. Thus, mission as regards the one to whom it is sent implies two things, the indwelling of grace, and a certain renewal by grace. Thus the invisible mission is sent to all in whom are to be found these two conditions.
Reply to Objection: 1. The invisible mission was directed to the Old Testament Fathers, as appears from what Augustine says (De Trin. iv, 20), that the invisible mission of the Son "is in man and with men. This was done in former times with the Fathers and the Prophets." Thus the words, "the Spirit was not yet given," are to be applied to that giving accompanied with a visible sign which took place on the day of Pentecost.
2. The invisible mission takes place also as regards progress in virtue or increase of grace. Hence Augustine says (De Trin. iv, 20), that "the Son is sent to each one when He is known and perceived by anyone, so far as He can be known and perceived according to the capacity of the soul, whether journeying towards God, or united perfectly to Him." Such invisible mission, however, chiefly occurs as regards anyone's proficiency in the performance of a new act, or in the acquisition of a new state of grace; as, for example, the proficiency in reference to the gift of miracles or of prophecy, or in the fervor of charity leading a man to expose himself to the danger of martyrdom, or to renounce his possessions, or to undertake any arduous work.
3. The invisible mission is directed to the blessed at the very beginning of their beatitude. The invisible mission is made to them subsequently, not by "intensity" of grace, but by the further revelation of mysteries; which goes on till the day of judgment. Such an increase is by the "extension" of grace, because it extends to a greater number of objects. To Christ the invisible mission was sent at the first moment of His conception; but not afterwards, since from the beginning of His conception He was filled with all wisdom and grace.
4. Grace resides instrumentally in the sacraments of the New Law, as the form of a thing designed resides in the instruments of the art designing, according to a process flowing from the agent to the passive object. But mission is only spoken of as directed to its term. Hence the mission of the divine person is not sent to the sacraments, but to those who receive grace through the sacraments.
Objection: 1. It would seem that the Holy Ghost is not fittingly sent in a visible manner. For the Son as visibly sent to the world is said to be less than the Father. But the Holy Ghost is never said to be less than the Father. Therefore the Holy Ghost is not fittingly sent in a visible manner.
2. Further, the visible mission takes place by way of union to a visible creature, as the Son's mission according to the flesh. But the Holy Ghost did not assume any visible creature; and hence it cannot be said that He exists otherwise in some creatures than in others, unless perhaps as in a sign, as He is also present in the sacraments, and in all the figures of the law. Thus the Holy Ghost is either not sent visibly at all, or His visible mission takes place in all these things.
3. Further, every visible creature is an effect showing forth the whole Trinity. Therefore the Holy Ghost is not sent by reason of those visible creatures more than any other person.
4. Further, the Son was visibly sent by reason of the noblest kind of creature---namely, the human nature. Therefore if the Holy Ghost is sent visibly, He ought to be sent by reason of rational creatures.
5. Further, whatever is done visibly by God is dispensed by the ministry of the angels; as Augustine says (De Trin. iii, 4,5,9). So visible appearances, if there have been any, came by means of the angels. Thus the angels are sent, and not the Holy Ghost.
6. Further, the Holy Ghost being sent in a visible manner is only for the purpose of manifesting the invisible mission; as invisible things are made known by the visible. So those to whom the invisible mission was not sent, ought not to receive the visible mission; and to all who received the invisible mission, whether in the New or in the Old Testament, the visible mission ought likewise to be sent; and this is clearly false. Therefore the Holy Ghost is not sent visibly.
On the contrary It is said (Mt 3,16) that, when our Lord was baptized, the Holy Ghost descended upon Him in the shape of a dove.
I answer that God provides for all things according to the nature of each thing. Now the nature of man requires that he be led to the invisible by visible things, as explained above (Question , Article ). Wherefore the invisible things of God must be made manifest to man by the things that are visible. As God, therefore, in a certain way has demonstrated Himself and His eternal processions to men by visible creatures, according to certain signs; so was it fitting that the invisible missions also of the divine persons should be made manifest by some visible creatures.
This mode of manifestation applies in different ways to the Son and to the Holy Ghost. For it belongs to the Holy Ghost, Who proceeds as Love, to be the gift of sanctification; to the Son as the principle of the Holy Ghost, it belongs to the author of this sanctification. Thus the Son has been sent visibly as the author of sanctification; the Holy Ghost as the sign of sanctification.
Reply to Objection: 1. The Son assumed the visible creature, wherein He appeared, into the unity of His person, so that whatever can be said of that creature can be said of the Son of God; and so, by reason of the nature assumed, the Son is called less than the Father. But the Holy Ghost did not assume the visible creature, in which He appeared, into the unity of His person; so that what is said of it cannot be predicated of Him. Hence He cannot be called less than the Father by reason of any visible creature.
2. The visible mission of the Holy Ghost does not apply to the imaginary vision which is that of prophecy; because as Augustine says (De Trin. ii, 6): "The prophetic vision is not displayed to corporeal eyes by corporeal shapes, but is shown in the spirit by the spiritual images of bodies. But whoever saw the dove and the fire, saw them by their eyes. Nor, again, has the Holy Ghost the same relation to these images that the Son has to the rock, because it is said, "The rock was Christ" (1Co 10,4). For that rock was already created, and after the manner of an action was named Christ, Whom it typified; whereas the dove and the fire suddenly appeared to signify only what was happening. They seem, however, to be like to the flame of the burning bush seen by Moses and to the column which the people followed in the desert, and to the lightning and thunder issuing forth when the law was given on the mountain. For the purpose of the bodily appearances of those things was that they might signify, and then pass away." Thus the visible mission is neither displayed by prophetic vision, which belongs to the imagination, and not to the body, nor by the sacramental signs of the Old and New Testament, wherein certain pre-existing things are employed to signify something. But the Holy Ghost is said to be sent visibly, inasmuch as He showed Himself in certain creatures as in signs especially made for that purpose.
3. Although the whole Trinity makes those creatures, still they are made in order to show forth in some special way this or that person. For as the Father, Son and Holy Ghost are signified by diverse names, so also can They each one be signified by different things; although neither separation nor diversity exists amongst Them.
4. It was necessary for the Son to be declared as the author of sanctification, as explained above. Thus the visible mission of the Son was necessarily made according to the rational nature to which it belongs to act, and which is capable of sanctification; whereas any other creature could be the sign of sanctification. Nor was such a visible creature, formed for such a purpose, necessarily assumed by the Holy Ghost into the unity of His person, since it was not assumed or used for the purpose of action, but only for the purpose of a sign; and so likewise it was not required to last beyond what its use required.
5. Those visible creatures were formed by the ministry of the angels, not to signify the person of an angel, but to signify the Person of the Holy Ghost. Thus, as the Holy Ghost resided in those visible creatures as the one signified in the sign, on that account the Holy Ghost is said to be sent visibly, and not as an angel.
6. It is not necessary that the invisible mission should always be made manifest by some visible external sign; but, as is said (1Co 12,7)---"the manifestation of the Spirit is given to every man unto profit"---that is, of the Church. This utility consists in the confirmation and propagation of the faith by such visible signs. This has been done chiefly by Christ and by the apostles, according to He 2,3, "which having begun to be declared by the Lord, was confirmed unto us by them that heard."
Thus in a special sense, a mission of the Holy Ghost was directed to Christ, to the apostles, and to some of the early saints on whom the Church was in a way founded; in such a manner, however, that the visible mission made to Christ should show forth the invisible mission made to Him, not at that particular time, but at the first moment of His conception. The visible mission was directed to Christ at the time of His baptism by the figure of a dove, a fruitful animal, to show forth in Christ the authority of the giver of grace by spiritual regeneration; hence the Father's voice spoke, "This is My beloved Son" (Mt 3,17), that others might be regenerated to the likeness of the only Begotten. The Transfiguration showed it forth in the appearance of a bright cloud, to show the exuberance of doctrine; and hence it was said, "Hear ye Him" (Mt 17,5). To the apostles the mission was directed in the form of breathing to show forth the power of their ministry in the dispensation of the sacraments; and hence it was said, "Whose sins you shall forgive, they are forgiven" (Jn 20,23): and again under the sign of fiery tongues to show forth the office of teaching; whence it is said that, "they began to speak with divers tongues" (Ac 2,4). The visible mission of the Holy Ghost was fittingly not sent to the fathers of the Old Testament, because the visible mission of the Son was to be accomplished before that of the Holy Ghost; since the Holy Ghost manifests the Son, as the Son manifests the Father. Visible apparitions of the divine persons were, however, given to the Fathers of the Old Testament which, indeed, cannot be called visible missions; because, according to Augustine (De Trin. ii, 17), they were not sent to designate the indwelling of the divine person by grace, but for the manifestation of something else.
Summa Th. I EN Qu.42 a.5