Summa Th. III EN Qu.66 a.5

Whether this be a suitable form of Baptism: "I baptize thee in the name of the Father, and of the Son, and of the Holy Ghost"?

Objection: 1. It seems that this is not a suitable form of Baptism: "I baptize thee in the name of the Father, and of the Son, and of the Holy Ghost." For action should be ascribed to the principal agent rather than to the minister. Now the minister of a sacrament acts as an instrument, as stated above (Question [64], Article [1]); while the principal agent in Baptism is Christ, according to Jn 1,33, "He upon Whom thou shalt see the Spirit descending and remaining upon Him, He it is that baptizeth." It is therefore unbecoming for the minister to say, "I baptize thee": the more so that "Ego" [I] is understood in the word "baptizo" [I baptize], so that it seems redundant.
2. Further, there is no need for a man who does an action, to make mention of the action done; thus he who teaches, need not say, "I teach you." Now our Lord gave at the same time the precepts both of baptizing and of teaching, when He said (Mt 28,19): "Going, teach ye all nations," etc. Therefore there is no need in the form of Baptism to mention the action of baptizing.
3. Further, the person baptized sometimes does not understand the words; for instance, if he be deaf, or a child. But it is useless to address such a one; according to Si 32,6: "Where there is no hearing, pour not out words." Therefore it is unfitting to address the person baptized with these words: "I baptize thee."
4. Further, it may happen that several are baptized by several at the same time; thus the apostles on one day baptized three thousand, and on another, five thousand (Ac 2,4). Therefore the form of Baptism should not be limited to the singular number in the words, "I baptize thee": but one should be able to say, "We baptize you."
5. Further, Baptism derives its power from Christ's Passion. But Baptism is sanctified by the form. Therefore it seems that Christ's Passion should be mentioned in the form of Baptism.
6. Further, a name signifies a thing's property. But there are three Personal Properties of the Divine Persons, as stated in the FP, Question [32], Article [3]. Therefore we should not say, "in the name," but "in the names of the Father, and of the Son, and of the Holy Ghost."
7. Further, the Person of the Father is designated not only by the name Father, but also by that of "Unbegotten and Begetter"; and the Son by those of "Word," "Image," and "Begotten"; and the Holy Ghost by those of "Gift," "Love," and the "Proceeding One." Therefore it seems that Baptism is valid if conferred in these names.

On the contrary our Lord said (Mt 28,19): "Going . . . teach ye all nations, baptizing them in the name of the Father, and of the Son, and of the Holy Ghost."
I answer that Baptism receives its consecration from its form, according to Ep 5,26: "Cleansing it by the laver of water in the word of life." And Augustine says (De Unico Baptismo iv) that "Baptism is consecrated by the words of the Gospel." Consequently the cause of Baptism needs to be expressed in the baptismal form. Now this cause is twofold; the principal cause from which it derives its virtue, and this is the Blessed Trinity; and the instrumental cause, viz. the minister who confers the sacrament outwardly. Wherefore both causes should be expressed in the form of Baptism. Now the minister is designated by the words, "I baptize thee"; and the principal cause in the words, "in the name of the Father, and of the Son, and of the Holy Ghost." Therefore this is the suitable form of Baptism: "I baptize thee in the name of the Father, and of the Son, and of the Holy Ghost."

Reply to Objection: 1. Action is attributed to an instrument as to the immediate agent; but to the principal agent inasmuch as the instrument acts in virtue thereof. Consequently it is fitting that in the baptismal form the minister should be mentioned as performing the act of baptizing, in the words, "I baptize thee"; indeed, our Lord attributed to the ministers the act of baptizing, when He said: "Baptizing them," etc. But the principal cause is indicated as conferring the sacrament by His own power, in the words, "in the name of the Father, and of the Son, and of the Holy Ghost": for Christ does not baptize without the Father and the Holy Ghost.The Greeks, however, do not attribute the act of baptizing to the minister, in order to avoid the error of those who in the past ascribed the baptismal power to the baptizers, saying (1Co 1,12): "I am of Paul . . . and I of Cephas." Wherefore they use the form: "May the servant of Christ, N . . ., be baptized, in the name of the Father," etc. And since the action performed by the minister is expressed with the invocation of the Trinity, the sacrament is validly conferred. As to the addition of "Ego" in our form, it is not essential; but it is added in order to lay greater stress on the intention.
2. Since a man may be washed with water for several reasons, the purpose for which it is done must be expressed by the words of the form. And this is not done by saying: "In the name of the Father, and of the Son, and of the Holy Ghost"; because we are bound to do all things in that Name (Col 3,17). Wherefore unless the act of baptizing be expressed, either as we do, or as the Greeks do, the sacrament is not valid; according to the decretal of Alexander III: "If anyone dip a child thrice in the water in the name of the Father, and of the Son, and of the Holy Ghost, Amen, without saying, I baptize thee in the name of the Father, and of the Son, and of the Holy Ghost, Amen, the child is not baptized."
3. The words which are uttered in the sacramental forms, are said not merely for the purpose of signification, but also for the purpose of efficiency, inasmuch as they derive efficacy from that Word, by Whom "all things were made." Consequently they are becomingly addressed not only to men, but also to insensible creatures; for instance, when we say: "I exorcize thee, creature salt" (Roman Ritual).
4. Several cannot baptize one at the same time: because an action is multiplied according to the number of the agents, if it be done perfectly by each. So that if two were to combine, of whom one were mute, and unable to utter the words, and the other were without hands, and unable to perform the action, they could not both baptize at the same time, one saying the words and the other performing the action.On the other hand, in a case of necessity, several could be baptized at the same time; for no single one of them would receive more than one baptism. But it would be necessary, in that case, to say: "I baptize ye." Nor would this be a change of form, because "ye" is the same as "thee and thee." Whereas "we" does not mean "I and I," but "I and thou"; so that this would be a change of form.Likewise it would be a change of form to say, "I baptize myself": consequently no one can baptize himself. For this reason did Christ choose to be baptized by John (Extra, De Baptismo et ejus effectu, cap. Debitum).
5. Although Christ's Passion is the principal cause as compared to the minister, yet it is an instrumental cause as compared to the Blessed Trinity. For this reason the Trinity is mentioned rather than Christ's Passion.
6. Although there are three personal names of the three Persons, there is but one essential name. Now the Divine power which works in Baptism, pertains to the Essence; and therefore we say, "in the name," and not, "in the names."
7. Just as water is used in Baptism, because it is more commonly employed in washing, so for the purpose of designating the three Persons, in the form of Baptism, those names are chosen, which are generally used, in a particular language, to signify the Persons. Nor is the sacrament valid if conferred in any other names.

Whether Baptism can be conferred in the name of Christ?

Objection: 1. It seems that Baptism can be conferred in the name of Christ. For just as there is "one Faith," so is there "one Baptism" (Ep 4,5). But it is related (Ac 8,12) that "in the name of Jesus Christ they were baptized, both men and women." Therefore now also can Baptism be conferred in the name of Christ.
2. Further, Ambrose says (De Spir. Sanct. i): "If you mention Christ, you designate both the Father by Whom He was anointed, and the Son Himself, Who was anointed, and the Holy Ghost with Whom He was anointed." But Baptism can be conferred in the name of the Trinity: therefore also in the name of Christ.
3. Further, Pope Nicholas I, answering questions put to him by the Bulgars, said: "Those who have been baptized in the name of the Trinity, or only in the name of Christ, as we read in the Acts of the Apostles (it is all the same, as Blessed Ambrose saith), must not be rebaptized." But they would be baptized again if they had not been validly baptized with that form. Therefore Baptism can be celebrated in the name of Christ by using this form: "I baptize thee in the name of Christ."

On the contrary Pope Pelagius II wrote to the Bishop Gaudentius: "If any people living in your Worship's neighborhood, avow that they have been baptized in the name of the Lord only, without any hesitation baptize them again in the name of the Blessed Trinity, when they come in quest of the Catholic Faith." Didymus, too, says (De Spir. Sanct.): "If indeed there be such a one with a mind so foreign to faith as to baptize while omitting one of the aforesaid names," viz. of the three Persons, "he baptizes invalidly."
I answer that As stated above (Question [64], Article [3]), the sacraments derive their efficacy from Christ's institution. Consequently, if any of those things be omitted which Christ instituted in regard to a sacrament, it is invalid; save by special dispensation of Him Who did not bind His power to the sacraments. Now Christ commanded the sacrament of Baptism to be given with the invocation of the Trinity. And consequently whatever is lacking to the full invocation of the Trinity, destroys the integrity of Baptism.Nor does it matter that in the name of one Person another is implied, as the name of the Son is implied in that of the Father, or that he who mentions the name of only one Person may believe aright in the Three; because just as a sacrament requires sensible matter, so does it require a sensible form. Hence, for the validity of the sacrament it is not enough to imply or to believe in the Trinity, unless the Trinity be expressed in sensible words. For this reason at Christ's Baptism, wherein was the source of the sanctification of our Baptism, the Trinity was present in sensible signs: viz. the Father in the voice, the Son in the human nature, the Holy Ghost in the dove.

Reply to Objection: 1. It was by a special revelation from Christ that in the primitive Church the apostles baptized in the name of Christ; in order that the name of Christ, which was hateful to Jews and Gentiles, might become an object of veneration, in that the Holy Ghost was given in Baptism at the invocation of that Name.
2. Ambrose here gives this reason why exception could, without inconsistency, be allowed in the primitive Church; namely, because the whole Trinity is implied in the name of Christ, and therefore the form prescribed by Christ in the Gospel was observed in its integrity, at least implicitly.
3. Pope Nicolas confirms his words by quoting the two authorities given in the preceding objections: wherefore the answer to this is clear from the two solutions given above.

Whether immersion in water is necessary for Baptism?

Objection: 1. It seems that immersion in water is necessary for Baptism. Because it is written (Ep 4,5): "One faith, one baptism." But in many parts of the world the ordinary way of baptizing is by immersion. Therefore it seems that there can be no Baptism without immersion.
2. Further, the Apostle says (Rm 6,3-4): "All we who are baptized in Christ Jesus, are baptized in His death: for we are buried together with Him, by Baptism into death." But this is done by immersion: for Chrysostom says on Jn 3,5: "Unless a man be born again of water and the Holy Ghost," etc.: "When we dip our heads under the water as in a kind of tomb, our old man is buried, and being submerged, is hidden below, and thence he rises again renewed." Therefore it seems that immersion is essential to Baptism.
3. Further, if Baptism is valid without total immersion of the body, it would follow that it would be equally sufficient to pour water over any part of the body. But this seems unreasonable; since original sin, to remedy which is the principal purpose of Baptism, is not in only one part of the body. Therefore it seems that immersion is necessary for Baptism, and that mere sprinkling is not enough.

On the contrary It is written (He 10,22): "Let us draw near with a true heart in fulness of faith, having our hearts sprinkled from an evil conscience, and our bodies washed with clean water."
I answer that In the sacrament of Baptism water is put to the use of a washing of the body, whereby to signify the inward washing away of sins. Now washing may be done with water not only by immersion, but also by sprinkling or pouring. And, therefore, although it is safer to baptize by immersion, because this is the more ordinary fashion, yet Baptism can be conferred by sprinkling or also by pouring, according to Ez 36,25: "I will pour upon you clean water," as also the Blessed Lawrence is related to have baptized. And this especially in cases of urgency: either because there is a great number to be baptized, as was clearly the case in Ac 2 Ac 4, where we read that on one day three thousand believed, and on another five thousand: or through there being but a small supply of water, or through feebleness of the minister, who cannot hold up the candidate for Baptism; or through feebleness of the candidate, whose life might be endangered by immersion. We must therefore conclude that immersion is not necessary for Baptism.

Reply to Objection: 1. What is accidental to a thing does not diversify its essence. Now bodily washing with water is essential to Baptism: wherefore Baptism is called a "laver," according to Ep 5,26: "Cleansing it by the laver of water in the word of life." But that the washing be done this or that way, is accidental to Baptism. And consequently such diversity does not destroy the oneness of Baptism.
2. Christ's burial is more clearly represented by immersion: wherefore this manner of baptizing is more frequently in use and more commendable. Yet in the other ways of baptizing it is represented after a fashion, albeit not so clearly; for no matter how the washing is done, the body of a man, or some part thereof, is put under water, just as Christ's body was put under the earth.
3. The principal part of the body, especially in relation to the exterior members, is the head, wherein all the senses, both interior and exterior, flourish. And therefore, if the whole body cannot be covered with water, because of the scarcity of water, or because of some other reason, it is necessary to pour water over the head, in which the principle of animal life is made manifest.And although original sin is transmitted through the members that serve for procreation, yet those members are not to be sprinkled in preference to the head, because by Baptism the transmission of original sin to the offspring by the act of procreation is not deleted, but the soul is freed from the stain and debt of sin which it has contracted. Consequently that part of the body should be washed in preference, in which the works of the soul are made manifest.Nevertheless in the Old Law the remedy against original sin was affixed to the member of procreation; because He through Whom original sin was to be removed, was yet to be born of the seed of Abraham, whose faith was signified by circumcision according to Rm 4,11.

Whether trine immersion is essential to Baptism?


Objection: 1. It seems that trine immersion is essential to Baptism. For Augustine says in a sermon on the Symbol, addressed to the Neophytes: "Rightly were you dipped three times, since you were baptized in the name of the Trinity. Rightly were you dipped three times, because you were baptized in the name of Jesus Christ, Who on the third day rose again from the dead. For that thrice repeated immersion reproduces the burial of the Lord by which you were buried with Christ in Baptism." Now both seem to be essential to Baptism, namely, that in Baptism the Trinity of Persons should be signified, and that we should be conformed to Christ's burial. Therefore it seems that trine immersion is essential to Baptism.
2. Further, the sacraments derive their efficacy from Christ's mandate. But trine immersion was commanded by Christ: for Pope Pelagius II wrote to Bishop Gaudentius: "The Gospel precept given by our Lord God Himself, our Saviour Jesus Christ, admonishes us to confer the sacrament of Baptism to each one in the name of the Trinity and also with trine immersion." Therefore, just as it is essential to Baptism to call on the name of the Trinity, so is it essential to baptize by trine immersion.
3. Further, if trine immersion be not essential to Baptism, it follows that the sacrament of Baptism is conferred at the first immersion; so that if a second or third immersion be added, it seems that Baptism is conferred a second or third time. which is absurd. Therefore one immersion does not suffice for the sacrament of Baptism, and trine immersion is essential thereto.

On the contrary Gregory wrote to the Bishop Leander: "It cannot be in any way reprehensible to baptize an infant with either a trine or a single immersion: since the Trinity can be represented in the three immersions, and the unity of the Godhead in one immersion."I answer that As stated above (Article [7], ad 1), washing with water is of itself required for Baptism, being essential to the sacrament: whereas the mode of washing is accidental to the sacrament. Consequently, as Gregory in the words above quoted explains, both single and trine immersion are lawful considered in themselves; since one immersion signifies the oneness of Christ's death and of the Godhead; while trine immersion signifies the three days of Christ's burial, and also the Trinity of Persons.But for various reasons, according as the Church has ordained, one mode has been in practice, at one time, the other at another time. For since from the very earliest days of the Church some have had false notions concerning the Trinity, holding that Christ is a mere man, and that He is not called the "Son of God" or "God" except by reason of His merit, which was chiefly in His death; for this reason they did not baptize in the name of the Trinity, but in memory of Christ's death, and with one immersion. And this was condemned in the early Church. Wherefore in the Apostolic Canons (xlix) we read: "If any priest or bishop confer baptism not with the trine immersion in the one administration, but with one immersion, which baptism is said to be conferred by some in the death of the Lord, let him be deposed": for our Lord did not say, "Baptize ye in My death," but "In the name of the Father and of the Son, and of the Holy Ghost."Later on, however, there arose the error of certain schismatics and heretics who rebaptized: as Augustine (Super. Joan., cf. De Haeres. lxix) relates of the Donatists. Wherefore, in detestation of their error, only one immersion was ordered to be made, by the (fourth) council of Toledo, in the acts of which we read: "In order to avoid the scandal of schism or the practice of heretical teaching let us hold to the single baptismal immersion."But now that this motive has ceased, trine immersion is universally observed in Baptism: and consequently anyone baptizing otherwise would sin gravely, through not following the ritual of the Church. It would, however, be valid Baptism.

Reply to Objection: 1. The Trinity acts as principal agent in Baptism. Now the likeness of the agent enters into the effect, in regard to the form and not in regard to the matter. Wherefore the Trinity is signified in Baptism by the words of the form. Nor is it essential for the Trinity to be signified by the manner in which the matter is used; although this is done to make the signification clearer.In like manner Christ's death is sufficiently represented in the one immersion. And the three days of His burial were not necessary for our salvation, because even if He had been buried or dead for one day, this would have been enough to consummate our redemption: yet those three days were ordained unto the manifestation of the reality of His death, as stated above (Question [53], Article [2]). It is therefore clear that neither on the part of the Trinity, nor on the part of Christ's Passion, is the trine immersion essential to the sacrament.
2. Pope Pelagius understood the trine immersion to be ordained by Christ in its equivalent; in the sense that Christ commanded Baptism to be conferred "in the name of the Father, and of the Son, and of the Holy Ghost." Nor can we argue from the form to the use of the matter, as stated above (ad 1).
3. As stated above (Question [64], Article [8]), the intention is essential to Baptism. Consequently, one Baptism results from the intention of the Church's minister, who intends to confer one Baptism by a trine immersion. Wherefore Jerome says on Ep 4,5-6: "Though the Baptism," i.e. the immersion, "be thrice repeated, on account of the mystery of the Trinity, yet it is reputed as one Baptism."If, however, the intention were to confer one Baptism at each immersion together with the repetition of the words of the form, it would be a sin, in itself, because it would be a repetition of Baptism.

Whether Baptism may be reiterated?

Objection: 1. It seems that Baptism may be reiterated. For Baptism was instituted, seemingly, in order to wash away sins. But sins are reiterated. Therefore much more should Baptism be reiterated: because Christ's mercy surpasses man's guilt.
2. Further, John the Baptist received special commendation from Christ, Who said of him (Mt 11,11): "There hath not risen among them that are born of women, a greater than John the Baptist." But those whom John had baptized were baptized again, according to Ac 19,1-7, where it is stated that Paul rebaptized those who had received the Baptism of John. Much more, therefore, should those be rebaptized, who have been baptized by heretics or sinners.
3. Further, it was decreed in the Council of Nicaea (Can. xix) that if "any of the Paulianists or Cataphrygians should be converted to the Catholic Church, they were to be baptized": and this seemingly should be said in regard to other heretics. Therefore those whom the heretics have baptized, should be baptized again.
4. Further, Baptism is necessary for salvation. But sometimes there is a doubt about the baptism of those who really have been baptized. Therefore it seems that they should be baptized again.
5. Further, the Eucharist is a more perfect sacrament than Baptism, as stated above (Question [65], Article [3]). But the sacrament of the Eucharist is reiterated. Much more reason, therefore, is there for Baptism to be reiterated.

On the contrary It is written, (Ep 4,5): "One faith, one Baptism."
I answer that Baptism cannot be reiterated.First, because Baptism is a spiritual regeneration; inasmuch as a man dies to the old life, and begins to lead the new life. Whence it is written (Jn 3,5): "Unless a man be born again of water and the Holy Ghost, He cannot see [Vulg.: 'enter into'] the kingdom of God." Now one man can be begotten but once. Wherefore Baptism cannot be reiterated, just as neither can carnal generation. Hence Augustine says on Jn 3,4: "'Can he enter a second time into his mother's womb and be born again': So thou," says he, "must understand the birth of the Spirit, as Nicodemus understood the birth of the flesh . . . . As there is no return to the womb, so neither is there to Baptism."Secondly, because "we are baptized in Christ's death," by which we die unto sin and rise again unto "newness of life" (Rm 6,3-4). Now "Christ died" but "once" (Rm 6,10). Wherefore neither should Baptism be reiterated. For this reason (He 6,6) is it said against some who wished to be baptized again: "Crucifying again to themselves the Son of God"; on which the gloss observes: "Christ's one death hallowed the one Baptism."Thirdly, because Baptism imprints a character, which is indelible, and is conferred with a certain consecration. Wherefore, just as other consecrations are not reiterated in the Church, so neither is Baptism. This is the view expressed by Augustine, who says (Contra Epist. Parmen. ii) that "the military character is not renewed": and that "the sacrament of Christ is not less enduring than this bodily mark, since we see that not even apostates are deprived of Baptism, since when they repent and return they are not baptized anew."Fourthly, because Baptism is conferred principally as a remedy against original sin. Wherefore, just as original sin is not renewed, so neither is Baptism reiterated, for as it is written (Rm 5,18), "as by the offense of one, unto all men to condemnation, so also by the justice of one, unto all men to justification of life."

Reply to Objection: 1. Baptism derives its efficacy from Christ's Passion, as stated above (Article [2], ad 1). Wherefore, just as subsequent sins do not cancel the virtue of Christ's Passion, so neither do they cancel Baptism, so as to call for its repetition. on the other hand the sin which hindered the effect of Baptism is blotted out on being submitted to Penance.
2. As Augustine says on Jn 1,33: "'And I knew Him not': Behold; after John had baptized, Baptism was administered; after a murderer has baptized, it is not administered: because John gave his own Baptism; the murderer, Christ's; for that sacrament is so sacred, that not even a murderer's administration contaminates it."
3. The Paulianists and Cataphrygians used not to baptize in the name of the Trinity. Wherefore Gregory, writing to the Bishop Quiricus, says: "Those heretics who are not baptized in the name of the Trinity, such as the Bonosians and Cataphrygians" (who were of the same mind as the Paulianists), "since the former believe not that Christ is God" (holding Him to be a mere man), "while the latter," i.e. the Cataphrygians, "are so perverse as to deem a mere man," viz. Montanus, "to be the Holy Ghost: all these are baptized when they come to holy Church, for the baptism which they received while in that state of error was no Baptism at all, not being conferred in the name of the Trinity." On the other hand, as set down in De Eccles. Dogm. xxii: "Those heretics who have been baptized in the confession of the name of the Trinity are to be received as already baptized when they come to the Catholic Faith."
4. According to the Decretal of Alexander III: "Those about whose Baptism there is a doubt are to be baptized with these words prefixed to the form: 'If thou art baptized, I do not rebaptize thee; but if thou art not baptized, I baptize thee,' etc.: for that does not appear to be repeated, which is not known to have been done."
5. Both sacraments, viz. Baptism and the Eucharist, are a representation of our Lord's death and Passion, but not in the same way. For Baptism is a commemoration of Christ's death in so far as man dies with Christ, that he may be born again into a new life. But the Eucharist is a commemoration of Christ's death, in so far as the suffering Christ Himself is offered to us as the Paschal banquet, according to 1Co 5,7-8: "Christ our pasch is sacrificed; therefore let us feast." And forasmuch as man is born once, whereas he eats many times, so is Baptism given once, but the Eucharist frequently.

Whether the Church observes a suitable rite in baptizing?

Objection: 1. It seems that the Church observes an unsuitable rite in baptizing. For as Chrysostom (Chromatius, in Matth. 3:15) says: "The waters of Baptism would never avail to purge the sins of them that believe, had they not been hallowed by the touch of our Lord's body." Now this took place at Christ's Baptism, which is commemorated in the Feast of the Epiphany. Therefore solemn Baptism should be celebrated at the Feast of the Epiphany rather than on the eves of Easter and Whitsunday.
2. Further, it seems that several matters should not be used in the same sacrament. But water is used for washing in Baptism. Therefore it is unfitting that the person baptized should be anointed thrice with holy oil first on the breast, and then between the shoulders, and a third time with chrism on the top of the head.
3. Further, "in Christ Jesus . . . there is neither male nor female" (Ga 3,23) . . . "neither Barbarian nor Scythian" (Col 3,11), nor, in like manner, any other such like distinctions. Much less, therefore can a difference of clothing have any efficacy in the Faith of Christ. It is consequently unfitting to bestow a white garment on those who have been baptized.
4. Further, Baptism can be celebrated without such like ceremonies. Therefore it seems that those mentioned above are superfluous; and consequently that they are unsuitably inserted by the Church in the baptismal rite.

On the contrary The Church is ruled by the Holy Ghost, Who does nothing inordinate.
I answer that In the sacrament of Baptism something is done which is essential to the sacrament, and something which belongs to a certain solemnity of the sacrament. Essential indeed, to the sacrament are both the form which designates the principal cause of the sacrament; and the minister who is the instrumental cause; and the use of the matter, namely, washing with water, which designates the principal sacramental effect. But all the other things which the Church observes in the baptismal rite, belong rather to a certain solemnity of the sacrament.And these, indeed, are used in conjunction with the sacrament for three reasons. First, in order to arouse the devotion of the faithful, and their reverence for the sacrament. For if there were nothing done but a mere washing with water, without any solemnity, some might easily think it to be an ordinary washing.Secondly, for the instruction of the faithful. Because simple and unlettered folk need to be taught by some sensible signs, for instance, pictures and the like. And in this way by means of the sacramental ceremonies they are either instructed, or urged to seek the signification of such like sensible signs. And consequently, since, besides the principal sacramental effect, other things should be known about Baptism, it was fitting that these also should be represented by some outward signs.Thirdly, because the power of the devil is restrained, by prayers, blessings, and the like, from hindering the sacramental effect.

Reply to Objection: 1. Christ was baptized on the Epiphany with the Baptism of John, as stated above (Question [39], Article [2]), with which baptism, indeed, the faithful are not baptized, rather are they baptized with Christ's Baptism. This has its efficacy from the Passion of Christ, according to Rm 6,3: "We who are baptized in Christ Jesus, are baptized in His death"; and in the Holy Ghost, according to Jn 3,5: "Unless a man be born again of water and the Holy Ghost." Therefore it is that solemn Baptism is held in the Church, both on Easter Eve, when we commemorate our Lord's burial and resurrection; for which reason our Lord gave His disciples the commandment concerning Baptism as related by Matthew (28:19): and on Whitsun-eve, when the celebration of the Feast of the Holy Ghost begins; for which reason the apostles are said to have baptized three thousand on the very day of Pentecost when they had received the Holy Ghost.
2. The use of water in Baptism is part of the substance of the sacrament; but the use of oil or chrism is part of the solemnity. For the candidate is first of all anointed with Holy oil on the breast and between the shoulders, as "one who wrestles for God," to use Ambrose's expression (De Sacram. i): thus are prize-fighters wont to besmear themselves with oil. Or, as Innocent III says in a decretal on the Holy Unction: "The candidate is anointed on the breast, in order to receive the gift of the Holy Ghost, to cast off error and ignorance, and to acknowledge the true faith, since 'the just man liveth by faith'; while he is anointed between the shoulders, that he may be clothed with the grace of the Holy Ghost, lay aside indifference and sloth, and become active in good works; so that the sacrament of faith may purify the thoughts of his heart, and strengthen his shoulders for the burden of labor." But after Baptism, as Rabanus says (De Sacram. iii), "he is forthwith anointed on the head by the priest with Holy Chrism, who proceeds at once to offer up a prayer that the neophyte may have a share in Christ's kingdom, and be called a Christian after Christ." Or, as Ambrose says (De Sacram. iii), his head is anointed, because "the senses of a wise man are in his head" (Eccl 2:14): to wit, that he may "be ready to satisfy everyone that asketh" him to give "a reason of his faith" (1P 3,15 Innocent III, Decretal on Holy Unction).
3. This white garment is given, not as though it were unlawful for the neophyte to use others: but as a sign of the glorious resurrection, unto which men are born again by Baptism; and in order to designate the purity of life, to which he will be bound after being baptized, according to Rm 6,4: "That we may walk in newness of life."
4. Although those things that belong to the solemnity of a sacrament are not essential to it, yet are they not superfluous, since they pertain to the sacrament's wellbeing, as stated above.

Summa Th. III EN Qu.66 a.5