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 Rom. 4:11. _______________________
EIGHTH ARTICLE [III, Q. 66, Art. 8]
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.
Obj. 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.
Obj. 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 (A. 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."