owever, was the power of the keys
instituted, which is derived from Christ's Passion, and consequently
it was not yet ordained that a man should grieve for his sin, with
the purpose of submitting himself by confession and satisfaction to
the keys of the Church, in the hope of receiving forgiveness through
the power of Christ's Passion.

Reply Obj. 3: If we note carefully what our Lord said about the
necessity of Baptism (John 3:3, seqq.), we shall see that this was
said before His words about the necessity of Penance (Matt. 4:17);
because He spoke to Nicodemus about Baptism before the imprisonment
of John, of whom it is related afterwards (John 3:23, 24) that he
baptized, whereas His words about Penance were said after John was
cast into prison.

If, however, He had admonished men to do penance before admonishing
them to be baptized, this would be because also before Baptism some
kind of penance is required, according to the words of Peter (Acts
2:38): "Do penance, and be baptized, every one of you."

Reply Obj. 4: Christ did not use the Baptism which He instituted, but
was baptized with the baptism of John, as stated above (Q. 39, AA. 1,
2). Nor did He use it actively by administering it Himself, because
He "did not baptize" as a rule, "but His disciples" did, as related
in John 4:2, although it is to be believed that He baptized His
disciples, as Augustine asserts (Ep. cclxv, ad Seleuc.). But with
regard to His institution of this sacrament it was nowise fitting
that He should use it, neither by repenting Himself, in Whom there
was no sin, nor by administering the sacrament to others, since, in
order to show His mercy and power, He was wont to confer the effect
of this sacrament without the sacrament itself, as stated above (A.
5, ad 3). On the other hand, He both received and gave to others the
sacrament of the Eucharist, both in order to commend the excellence
of that sacrament, and because that sacrament is a memorial of His
Passion, in which Christ is both priest and victim.
_______________________

EIGHTH ARTICLE [III, Q. 84, Art. 8]

Whether Penance Should Last Till the End of Life?

Objection 1: It would seem that Penance should not last till the end
of life. Because Penance is ordained for the blotting out of sin. Now
the penitent receives forgiveness of his sins at once, according to
Ezech. 18:21: "If the wicked do penance for all his sins which he
hath committed . . . he shall live and shall not die.