Summa Th. III EN Qu.4 a.3
Objection: 1. It would seem that the Divine Person assumed a man. For it is written (Ps 64,5): "Blessed is he whom Thou hast chosen and taken to Thee," which a gloss expounds of Christ; and Augustine says (De Agone Christ. xi): "The Son of God assumed a man, and in him bore things human."
2. Further, the word "man" signifies a human nature. But the Son of God assumed a human nature. Therefore He assumed a man.
3. Further, the Son of God is a man. But He is not one of the men He did not assume, for with equal reason He would be Peter or any other man. Therefore He is the man whom He assumed.
On the contrary Is the authority of Felix, Pope and Martyr, which is quoted by the Council of Ephesus: "We believe in our Lord Jesus Christ, born of the Virgin Mary, because He is the Eternal Son and Word of God, and not a man assumed by God, in such sort that there is another besides Him. For the Son of God did not assume a man, so that there be another besides Him."
I answer that As has been said above (Article ), what is assumed is not the term of the assumption, but is presupposed to the assumption. Now it was said (Question , Articles ,2) that the individual to Whom the human nature is assumed is none other than the Divine Person, Who is the term of the assumption. Now this word "man" signifies human nature, as it is in a suppositum, because, as Damascene says (De Fide Orth. iii, 4,11), this word God signifies Him Who has human nature. And hence it cannot properly be said that the Son assumed a man, granted (as it must be, in fact) that in Christ there is but one suppositum and one hypostasis. But according to such as hold that there are two hypostases or two supposita in Christ, it may fittingly and properly be said that the Son of God assumed a man. Hence the first opinion quoted in Sent. iii, D. 6, grants that a man was assumed. But this opinion is erroneous, as was said above (Question , Article ).
Reply to Objection: 1. These phrases are not to be taken too literally, but are to be loyally explained, wherever they are used by holy doctors; so as to say that a man was assumed, inasmuch as his nature was assumed; and because the assumption terminated in this---that the Son of God is man.
2. The word "man" signifies human nature in the concrete, inasmuch as it is in a suppositum; and hence, since we cannot say a suppositum was assumed, so we cannot say a man was assumed.
3. The Son of God is not the man whom He assumed, but the man whose nature He assumed.
Objection: 1. It would seem that the Son of God ought to have assumed human nature abstracted from all individuals. For the assumption of human nature took place for the common salvation of all men; hence it is said of Christ (1Tm 4,10) that He is "the Saviour of all men, especially of the faithful." But nature as it is in individuals withdraws from its universality. Therefore the Son of God ought to have assumed human nature as it is abstracted from all individuals.
2. Further, what is noblest in all things ought to be attributed to God. But in every genus what is of itself is best. Therefore the Son of God ought to have assumed self-existing [per se] man, which, according to Platonists, is human nature abstracted from its individuals. Therefore the Son of God ought to have assumed this.
3. Further, human nature was not assumed by the Son of God in the concrete as is signified by the word "man," as was said above (Article ). Now in this way it signifies human nature as it is in individuals, as is plain from what has been said (Article ). Therefore the Son of God assumed human nature as it is separated from individuals.
On the contrary Damascene says (De Fide Orth. iii, 11): "God the Word Incarnate did not assume a nature which exists in pure thought; for this would have been no Incarnation, but a false and fictitious Incarnation." But human nature as it is separated or abstracted from individuals is "taken to be a pure conception, since it does not exist in itself," as Damascene says (De Fide Orth. iii, 11). Therefore the Son of God did not assume human nature, as it is separated from individuals.
I answer that The nature of man or of any other sensible thing, beyond the being which it has in individuals, may be taken in two ways: first, as if it had being of itself, away from matter, as the Platonists held; secondly, as existing in an intellect either human or Divine. Now it cannot subsist of itself, as the Philosopher proves (Metaph. vii, 26,27,29,51), because sensible matter belongs to the specific nature of sensible things, and is placed in its definition, as flesh and bones in the definition of man. Hence human nature cannot be without sensible matter. Nevertheless, if human nature were subsistent in this way, it would not be fitting that it should be assumed by the Word of God. First, because this assumption is terminated in a Person, and it is contrary to the nature of a common form to be thus individualized in a person. Secondly, because to a common nature can only be attributed common and universal operations, according to which man neither merits nor demerits, whereas, on the contrary, the assumption took place in order that the Son of God, having assumed our nature, might merit for us. Thirdly, because a nature so existing would not be sensible, but intelligible. But the Son of God assumed human nature in order to show Himself in men's sight, according to Baruch 3:38: "Afterwards He was seen upon earth, and conversed with men."Likewise, neither could human nature have been assumed by the Son of God, as it is in the Divine intellect, since it would be none other than the Divine Nature; and, according to this, human nature would be in the Son of God from eternity. Neither can we say that the Son of God assumed human nature as it is in a human intellect, for this would mean nothing else but that He is understood to assume a human nature; and thus if He did not assume it in reality, this would be a false understanding; nor would this assumption of the human nature be anything but a fictitious Incarnation, as Damascene says (De Fide Orth. iii, 11).
Reply to Objection: 1. The incarnate Son of God is the common Saviour of all, not by a generic or specific community, such as is attributed to the nature separated from the individuals, but by a community of cause, whereby the incarnate Son of God is the universal cause of human salvation.
2. Self-existing [per se] man is not to be found in nature in such a way as to be outside the singular, as the Platonists held, although some say Plato believed that the separate man was only in the Divine intellect. And hence it was not necessary for it to be assumed by the Word, since it had been with Him from eternity.
3. Although human nature was not assumed in the concrete, as if the suppositum were presupposed to the assumption, nevertheless it is assumed in an individual, since it is assumed so as to be in an individual.
Objection: 1. It would seem that the Son of God ought to have assumed human nature in all individuals. For what is assumed first and by itself is human nature. But what belongs essentially to a nature belongs to all who exist in the nature. Therefore it was fitting that human nature should be assumed by the Word of God in all its supposita.
2. Further, the Divine Incarnation proceeded from Divine Love; hence it is written (Jn 3,16): "God so loved the world as to give His only-begotten Son." But love makes us give ourselves to our friends as much as we can, and it was possible for the Son of God to assume several human natures, as was said above (Question , Article ), and with equal reason all. Hence it was fitting for the Son of God to assume human nature in all its supposita.
3. Further, a skilful workman completes his work in the shortest manner possible. But it would have been a shorter way if all men had been assumed to the natural sonship than for one natural Son to lead many to the adoption of sons, as is written Ga 4,5 (He 2,10). Therefore human nature ought to have been assumed by God in all its supposita.
On the contrary Damascene says (De Fide Orth. iii, 11) that the Son of God "did not assume human nature as a species, nor did He assume all its hypostases."
I answer that It was unfitting for human nature to be assumed by the Word in all its supposita. First, because the multitude of supposita of human nature, which are natural to it, would have been taken away. For since we must not see any other suppositum in the assumed nature, except the Person assuming, as was said above (Article ), if there was no human nature except what was assumed, it would follow that there was but one suppositum of human nature, which is the Person assuming. Secondly, because this would have been derogatory to the dignity of the incarnate Son of God, as He is the First-born of many brethren, according to the human nature, even as He is the First-born of all creatures according to the Divine, for then all men would be of equal dignity. Thirdly, because it is fitting that as one Divine suppositum is incarnate, so He should assume one human nature, so that on both sides unity might be found.
Reply to Objection: 1. To be assumed belongs to the human nature of itself, because it does not belong to it by reason of a person, as it belongs to the Divine Nature to assume by reason of the Person; not, however, that it belongs to it of itself as if belonging to its essential principles, or as its natural property in which manner it would belong to all its supposita.
2. The love of God to men is shown not merely in the assumption of human nature, but especially in what He suffered in human nature for other men, according to Rm 5,8: "But God commendeth His charity towards us; because when as yet we were sinners . . . Christ died for us," which would not have taken place had He assumed human nature in all its supposita.
3. In order to shorten the way, which every skilful workman does, what can be done by one must not be done by many. Hence it was most fitting that by one man all the rest should be saved.
Objection: 1. It would seem that it was not fitting for the Son of God to assume human nature of the stock of Adam, for the Apostle says (He 7,26): "For it was fitting that we should have such a high priest . . . separated from sinners." But He would have been still further separated from sinners had He not assumed human nature of the stock of Adam, a sinner. Hence it seems that He ought not to have assumed human nature of the stock of Adam.
2. Further, in every genus the principle is nobler than what is from the principle. Hence, if He wished to assume human nature, He ought to have assumed it in Adam himself.
3. Further, the Gentiles were greater sinners than the Jews, as a gloss says on Ga 2,15: "For we by nature are Jews, and not of the Gentiles, sinners." Hence, if He wished to assume human nature from sinners, He ought rather to have assumed it from the Gentiles than from the stock of Abraham, who was just.
On the contrary (Lc 3), the genealogy of our Lord is traced back to Adam.
I answer that As Augustine says (De Trin. xiii, 18): "God was able to assume human nature elsewhere than from the stock of Adam, who by his sin had fettered the whole human race; yet God judged it better to assume human nature from the vanquished race, and thus to vanquish the enemy of the human race." And this for three reasons: First, because it would seem to belong to justice that he who sinned should make amends; and hence that from the nature which he had corrupted should be assumed that whereby satisfaction was to be made for the whole nature. Secondly, it pertains to man's greater dignity that the conqueror of the devil should spring from the stock conquered by the devil. Thirdly, because God's power is thereby made more manifest, since, from a corrupt and weakened nature, He assumed that which was raised to such might and glory.
Reply to Objection: 1. Christ ought to be separated from sinners as regards sin, which He came to overthrow, and not as regards nature which He came to save, and in which "it behooved Him in all things to be made like to His brethren," as the Apostle says (He 2,17). And in this is His innocence the more wonderful, seeing that though assumed from a mass tainted by sin, His nature was endowed with such purity.
2. As was said above (ad 1) it behooved Him Who came to take away sins to be separated from sinners as regards sin, to which Adam was subject, whom Christ "brought out of his sin," as is written (Sg 10,2). For it behooved Him Who came to cleanse all, not to need cleansing Himself; just as in every genus of motion the first mover is immovable as regards that motion, and the first to alter is itself unalterable. Hence it was not fitting that He should assume human nature in Adam himself.
3. Since Christ ought especially to be separated from sinners as regards sin, and to possess the highest innocence, it was fitting that between the first sinner and Christ some just men should stand midway, in whom certain forecasts of (His) future holiness should shine forth. And hence, even in the people from whom Christ was to be born, God appointed signs of holiness, which began in Abraham, who was the first to receive the promise of Christ, and circumcision, as a sign that the covenant should be kept, as is written (Gn 17,11).
We must now consider the assumption of the parts of human nature; and under this head there are four points of inquiry:
(1) Whether the Son of God ought to have assumed a true body?
(2) Whether He ought to have assumed an earthly body, i.e. one of flesh and blood?
(3) Whether He ought to have assumed a soul?
(4) Whether He ought to have assumed an intellect?
Objection: 1. It would seem that the Son of God did not assume a true body. For it is written (Ph 2,7), that He was "made in the likeness of men." But what is something in truth is not said to be in the likeness thereof. Therefore the Son of God did not assume a true body.
2. Further, the assumption of a body in no way diminishes the dignity of the Godhead; for Pope Leo says (Serm. de Nativ.) that "the glorification did not absorb the lesser nature, nor did the assumption lessen the higher." But it pertains to the dignity of God to be altogether separated from bodies. Therefore it seems that by the assumption God was not united to a body.
3. Further, signs ought to correspond to the realities. But the apparitions of the Old Testament which were signs of the manifestation of Christ were not in a real body, but by visions in the imagination, as is plain from Is 60,1: "I saw the Lord sitting," etc. Hence it would seem that the apparition of the Son of God in the world was not in a real body, but only in imagination.
On the contrary Augustine says (Qq. lxxxiii, qu. 13): "If the body of Christ was a phantom, Christ deceived us, and if He deceived us, He is not the Truth. But Christ is the Truth. Therefore His body was not a phantom." Hence it is plain that He assumed a true body.
I answer that As is said (De Eccles. Dogm. ii). The Son of God was not born in appearance only, as if He had an imaginary body; but His body was real. The proof of this is threefold. First, from the essence of human nature to which it pertains to have a true body. Therefore granted, as already proved (Question , Article ), that it was fitting for the Son of God to assume human nature, He must consequently have assumed a real body. The second reason is taken from what was done in the mystery of the Incarnation. For if His body was not real but imaginary, He neither underwent a real death, nor of those things which the Evangelists recount of Him, did He do any in very truth, but only in appearance; and hence it would also follow that the real salvation of man has not taken place; since the effect must be proportionate to the cause. The third reason is taken from the dignity of the Person assuming, Whom it did not become to have anything fictitious in His work, since He is the Truth. Hence our Lord Himself deigned to refute this error (Lc 24,37 Lc 24,39), when the disciples, "troubled and frighted, supposed that they saw a spirit," and not a true body; wherefore He offered Himself to their touch, saying: "Handle, and see; for a spirit hath not flesh and bones, as you see Me to have."
Reply to Objection: 1. This likeness indicates the truth of the human nature in Christ---just as all that truly exist in human nature are said to be like in species---and not a mere imaginary likeness. In proof of this the Apostle subjoins (Ph 2,8) that He became "obedient unto death, even to the death of the cross"; which would have been impossible, had it been only an imaginary likeness.
2. By assuming a true body the dignity of the Son of God is nowise lessened. Hence Augustine [*Fulgentius] says (De Fide ad Petrum ii): "He emptied Himself, taking the form of a servant, that He might become a servant; yet did He not lose the fulness of the form of God." For the Son of God assumed a true body, not so as to become the form of a body, which is repugnant to the Divine simplicity and purity---for this would be to assume a body to the unity of the nature, which is impossible, as is plain from what has been stated above (Question , Article ): but, the natures remaining distinct, He assumed a body to the unity of Person.
3. The figure ought to correspond to the reality as regards the likeness and not as regards the truth of the thing. For if they were alike in all points, it would no longer be a likeness but the reality itself, as Damascene says (De Fide Orth. iii, 26). Hence it was more fitting that the apparitions of the old Testament should be in appearance only, being figures; and that the apparition of the Son of God in the world should be in a real body, being the thing prefigured by these figures. Hence the Apostle says (Col 2,17): "Which are a shadow of things to come, but the body is Christ's."
Objection: 1. It would seem that Christ had not a carnal or earthly, but a heavenly body. For the Apostle says (1Co 15,41): "The first man was of the earth, earthy; the second man from heaven, heavenly." But the first man, i.e. Adam, was of the earth as regards his body, as is plain from Gn 1. Therefore the second man, i.e. Christ, was of heaven as regards the body.
2. Further, it is said (1Co 15,50): "Flesh and blood shall not [Vulg.: 'cannot'] possess the kingdom of God." But the kingdom of God is in Christ chiefly. Therefore there is no flesh or blood in Him, but rather a heavenly body.
3. Further, whatever is best is to be attributed to God. But of all bodies a heavenly body is the best. Therefore it behooved Christ to assume such a body.
On the contrary our Lord says (Lc 24,39): "A spirit hath not flesh and bones, as you see Me to have." Now flesh and bones are not of the matter of heavenly bodies, but are composed of the inferior elements. Therefore the body of Christ was not a heavenly, but a carnal and earthly body.
I answer that By the reasons which proved that the body of Christ was not an imaginary one, it may also be shown that it was not a heavenly body. First, because even as the truth of the human nature of Christ would not have been maintained had His body been an imaginary one, such as Manes supposed, so likewise it would not have been maintained if we supposed, as did Valentine, that it was a heavenly body. For since the form of man is a natural thing, it requires determinate matter, to wit, flesh and bones, which must be placed in the definition of man, as is plain from the Philosopher (Metaph. vii, 39). Secondly, because this would lessen the truth of such things as Christ did in the body. For since a heavenly body is impassible and incorruptible, as is proved De Coel. i, 20, if the Son of God had assumed a heavenly body, He would not have truly hungered or thirsted, nor would he have undergone His passion and death. Thirdly, this would have detracted from God's truthfulness. For since the Son of God showed Himself to men, as if He had a carnal and earthly body, the manifestation would have been false, had He had a heavenly body. Hence (De Eccles. Dogm. ii) it is said: "The Son of God was born, taking flesh of the Virgin's body, and not bringing it with Him from heaven."
Reply to Objection: 1. Christ is said in two ways to have come down from heaven. First, as regards His Divine Nature; not indeed that the Divine Nature ceased to be in heaven, but inasmuch as He began to be here below in a new way, viz. by His assumed. nature, according to Jn 3,13: "No man hath ascended into heaven, but He that descended from heaven, the Son of Man, Who is in heaven."Secondly, as regards His body, not indeed that the very substance of the body of Christ descended from heaven, but that His body was formed by a heavenly power, i.e. by the Holy Ghost. Hence Augustine, explaining the passage quoted, says (Ad Orosium [*Dial. Qq. lxv, qu. 4, work of an unknown author]): "I call Christ a heavenly man because He was not conceived of human seed." And Hilary expounds it in the same way (De Trin. x).
2. Flesh and blood are not taken here for the substance of flesh and blood, but for the corruption of flesh, which was not in Christ as far as it was sinful; but as far as it was a punishment; thus, for a time, it was in Christ, that He might carry through the work of our redemption.
3. It pertains to the greatest glory of God to have raised a weak and earthly body to such sublimity. Hence in the General Council of Ephesus (P. II, Act. I) we read the saying of St. Theophilus: "Just as the best workmen are esteemed not merely for displaying their skill in precious materials, but very often because by making use of the poorest . . . lay and commonest earth, they show the power of their craft; so the best of all workmen, the Word of God, did not come down to us by taking a heavenly body of some most precious matter, but shewed the greatness of His skill in clay."
Objection: 1. It would seem that the Son of God did not assume a soul. For John has said, teaching the mystery of the Incarnation (Jn 1,14): "The Word was made flesh"---no mention being made of a soul. Now it is not said that "the Word was made flesh" as if changed to flesh, but because He assumed flesh. Therefore He seems not to have assumed a soul.
2. Further, a soul is necessary to the body, in order to quicken it. But this was not necessary for the body of Christ, as it would seem, for of the Word of God it is written (Ps 35,10): Lord, "with Thee is the fountain of life." Therefore it would seem altogether superfluous for the soul to be there, when the Word was present. But "God and nature do nothing uselessly," as the Philosopher says (De Coel. i, 32; ii, 56). Therefore the Word would seem not to have assumed a soul.
3. Further, by the union of soul and body is constituted the common nature, which is the human species. But "in the Lord Jesus Christ we are not to look for a common species," as Damascene says (De Fide Orth. iii, 3). Therefore He did not assume a soul.
On the contrary Augustine says (De Agone Christ. xxi): "Let us not hearken to such as say that only a human body was assumed by the Word of God; and take 'the Word was made flesh' to mean that the man had no soul nor any other part of a man, save flesh."
I answer that As Augustine says (De Haeres. 69,55), it was first of all the opinion of Arius and then of Apollinaris that the Son of God assumed only flesh, without a soul, holding that the Word took the place of a soul to the body. And consequently it followed that there were not two natures in Christ, but only one; for from a soul and body one human nature is constituted. But this opinion cannot hold, for three reasons. First, because it is counter to the authority of Scripture, in which our Lord makes mention of His soul, Mt 26,38: "My soul is sorrowful even unto death"; and Jn 10,18: "I have power to lay down My soul [animam meam: Douay: 'My life']." But to this Apollinaris replied that in these words soul is taken metaphorically, in which way mention is made in the Old Testament of the soul of God (Is 1,14): "My soul hateth your new moons and your solemnities." But, as Augustine says (Qq. lxxxiii, qu. 80), the Evangelists relate how Jesus wondered, was angered, sad, and hungry. Now these show that He had a true soul, just as that He ate, slept and was weary shows that He had a true human body: otherwise, if these things are a metaphor, because the like are said of God in the Old Testament, the trustworthiness of the Gospel story is undermined. For it is one thing that things were foretold in a figure, and another that historical events were related in very truth by the Evangelists. Secondly, this error lessens the utility of the Incarnation, which is man's liberation. For Augustine [*Vigilius Tapsensis] argues thus (Contra Felician. xiii): "If the Son of God in taking flesh passed over the soul, either He knew its sinlessness, and trusted it did not need a remedy; or He considered it unsuitable to Him, and did not bestow on it the boon of redemption; or He reckoned it altogether incurable, and was unable to heal it; or He cast it off as worthless and seemingly unfit for any use. Now two of these reasons imply a blasphemy against God. For how shall we call Him omnipotent, if He is unable to heal what is beyond hope? Or God of all, if He has not made our soul. And as regards the other two reasons, in one the cause of the soul is ignored, and in the other no place is given to merit. Is He to be considered to understand the cause of the soul, Who seeks to separate it from the sin of wilful transgression, enabled as it is to receive the law by the endowment of the habit of reason? Or how can His generosity be known to any one who says it was despised on account of its ignoble sinfulness? If you look at its origin, the substance of the soul is more precious than the body: but if at the sin of transgression, on account of its intelligence it is worse than the body. Now I know and declare that Christ is perfect wisdom, nor have I any doubt that He is most loving; and because of the first of these He did not despise what was better and more capable of prudence; and because of the second He protected what was most wounded." Thirdly, this position is against the truth of the Incarnation. For flesh and the other parts of man receive their species through the soul. Hence, if the soul is absent, there are no bones nor flesh, except equivocally, as is plain from the Philosopher (De Anima ii, 9; Metaph. vii, 34).
Reply to Objection: 1. When we say, "The Word was made flesh," "flesh" is taken for the whole man, as if we were to say, "The Word was made man," as Is 40,5: "All flesh together shall see that the mouth of the Lord hath spoken." And the whole man is signified by flesh, because, as is said in the authority quoted, the Son of God became visible by flesh; hence it is subjoined: "And we saw His glory." Or because, as Augustine says (Qq. lxxxiii, qu. 80), "in all that union the Word is the highest, and flesh the last and lowest. Hence, wishing to commend the love of God's humility to us, the Evangelist mentioned the Word and flesh, leaving the soul on one side, since it is less than the Word and nobler than flesh." Again, it was reasonable to mention flesh, which, as being farther away from the Word, was less assumable, as it would seem.
2. The Word is the fountain of life, as the first effective cause of life; but the soul is the principle of the life of the body, as its form. Now the form is the effect of the agent. Hence from the presence of the Word it might rather have been concluded that the body was animated, just as from the presence of fire it may be concluded that the body, in which fire adheres, is warm.
3. It is not unfitting, indeed it is necessary to say that in Christ there was a nature which was constituted by the soul coming to the body. But Damascene denied that in Jesus Christ there was a common species, i.e. a third something resulting from the Godhead and the humanity.
Objection: 1. It would seem that the Son of God did not assume a human mind or intellect. For where a thing is present, its image is not required. But man is made to God's image, as regards his mind, as Augustine says (De Trin. xiv, 3,6). Hence, since in Christ there was the presence of the Divine Word itself, there was no need of a human mind.
2. Further, the greater light dims the lesser. But the Word of God, Who is "the light, which enlighteneth every man that cometh into this world," as is written Jn 1,9, is compared to the mind as the greater light to the lesser; since our mind is a light, being as it were a lamp enkindled by the First Light (Pr 20,27): "The spirit of a man is the lamp of the Lord." Therefore in Christ Who is the Word of God, there is no need of a human mind.
3. Further, the assumption of human nature by the Word of God is called His Incarnation. But the intellect or human mind is nothing carnal, either in its substance or in its act. for it is not the act of a body, as is proved De Anima iii, 6. Hence it would seem that the Son of God did not assume a human mind.
On the contrary Augustine [*Fulgentius] says (De Fide ad Petrum xiv): "Firmly hold and nowise doubt that Christ the Son of God has true flesh and a rational soul of the same kind as ours, since of His flesh He says (Lc 24,39): 'Handle, and see; for a spirit hath not flesh and bones, as you see Me to have.' And He proves that He has a soul, saying (Jn 10,17): 'I lay down My soul [Douay: 'life'] that I may take it again.' And He proves that He has an intellect, saying (Mt 11,29): 'Learn of Me, because I am meek and humble of heart.' And God says of Him by the prophet (Is 52,13): 'Behold my servant shall understand.'"
I answer that As Augustine says (De Haeres. 49,50), "the Apollinarists thought differently from the Catholic Church concerning the soul of Christ, saying with the Arians, that Christ took flesh alone, without a soul; and on being overcome on this point by the Gospel witness, they went on to say that the mind was wanting to Christ's soul, but that the Word supplied its place." But this position is refuted by the same arguments as the preceding. First, because it runs counter to the Gospel story, which relates how He marveled (as is plain from Mt 8,10). Now marveling cannot be without reason, since it implies the collation of effect and cause, i.e. inasmuch as when we see an effect and are ignorant of its cause, we seek to know it, as is said Metaph. i, 2. Secondly, it is inconsistent with the purpose of the Incarnation, which is the justification of man from sin. For the human soul is not capable of sin nor of justifying grace except through the mind. Hence it was especially necessary for the mind to be assumed. Hence Damascene says (De Fide Orth. iii, 6) that "the Word of God assumed a body and an intellectual and rational soul," and adds afterwards: "The whole was united to the whole, that He might bestow salvation on me wholly; for what was not assumed is not curable." Thirdly, it is against the truth of the Incarnation. For since the body is proportioned to the soul as matter to its proper form, it is not truly human flesh if it is not perfected by human, i.e. a rational soul. And hence if Christ had had a soul without a mind, He would not have had true human flesh, but irrational flesh, since our soul differs from an animal soul by the mind alone. Hence Augustine says (Qq. lxxxiii, qu. 80) that from this error it would have followed that the Son of God "took an animal with the form of a human body," which, again, is against the Divine truth, which cannot suffer any fictitious untruth.
Reply to Objection: 1. Where a thing is by its presence, its image is not required to supply the place of the thing, as where the emperor is the soldiers do not pay homage to his image. Yet the image of a thing is required together with its presence, that it may be perfected by the presence of the thing, just as the image in the wax is perfected by the impression of the seal, and as the image of man is reflected in the mirror by his presence. Hence in order to perfect the human mind it was necessary that the Word should unite it to Himself.
2. The greater light dims the lesser light of another luminous body; but it does not dim, rather it perfects the light of the body illuminated---at the presence of the sun the light of the stars is put out, but the light of the air is perfected. Now the intellect or mind of man is, as it were, a light lit up by the light of the Divine Word; and hence by the presence of the Word the mind of man is perfected rather than overshadowed.
3. Although the intellective power is not the act of a body, nevertheless the essence of the human soul, which is the form of the body, requires that it should be more noble, in order that it may have the power of understanding; and hence it is necessary that a better disposed body should correspond to it.
Summa Th. III EN Qu.4 a.3