For whatever it’s worth, the following is from the Catechism of the Council of Trent. I found it at
cin.org/users/james/ebooks/master/trent/tsacr-b.htm
Institution Of Baptism
When these things have been explained, it will also be expedient to teach and remind the faithful that, in common with the other Sacraments, Baptism was instituted by Christ the Lord. On this subject the pastor should frequently teach and point out that there are two different periods of time which relate to Baptism, �� one the period of its institution by the Redeemer; the other, the establishment of the law regarding its reception.
Baptism Instituted At Christ’s Baptism
With regard to the former, it is clear that this Sacrament was instituted by our Lord when, having been baptised by John, He gave to water the power of sanctifying. St. Gregory Nazianzen and St. Augustine � testify that to water was then. imparted the power of regenerating to spiritual life. In another place St. Augustine says: From the moment that Christ is immersed in water, water washes away all sins. And again: The Lord is baptised, not because He had need to be cleansed, but in order that, by the contact of His pure flesh, He might purify the waters and impart to them the power of cleansing.
A very strong argument to prove that Baptism was then instituted by our Lord might be afforded by the fact the most Holy Trinity, in whose name Baptism is conferred, manifested Its divine presence on that occasion. The voice of the Father was heard, the Person of the Son was present, the Holy Ghost descended in the form of a dove; and the heavens, into which we are enabled to enter by Baptism, were thrown open.
Should anyone desire to know how our Lord has endowed water with a virtue so great, so divine, this indeed transcends the power of the human understanding. Yet this we can know, that when our Lord was baptised, water, by contact with His most holy and pure body, was consecrated to the salutary use of Baptism, in such a way, however, that, although instituted before the Passion, we must believe that this Sacrament derives all its virtue and efficacy from the Passion, which is the consummation, as it were, of all the actions of Christ.
Baptism Made Obligatory After Christ’s Resurrection
The second period to be distinguished, that is, the time when the law of Baptism was made, also admits of no doubt. Holy writers are unanimous in saying that after the Resurrection of our Lord, when He gave to His Apostles the command to go and teach all nations: baptising them in the name of the Father, and of the Son, and of the Holy Ghost, the law of Baptism became obligatory on all who were to be saved.
This is inferred from the authority of the Prince of the Apostles when he says: Who hath regenerated us into a lively hope, by the resurrection of Jesus Christ from the dead;’ and also from what Paul says of the Church: He delivered himself up for it: that he might sanctify it, cleansing it by the laver of water in the word of life. By both Apostles the obligation of Baptism seems to be referred to the time which followed the death of our Lord. Hence we can have no doubt that the words of the Saviour: Unless a man be born again of water and the Holy Ghost, he cannot enter into the kingdom of God, refer also to the same time which was to follow after His Passion.
