Summa Theologica III, Q. 68, A. 4.
Reply to Objection 2. As stated above (1, ad 2; 68, 2) man receives the forgiveness of sins before Baptism in so far as he has Baptism of desire, explicitly or implicitly ; and yet when he actually receives Baptism, he receives a fuller remission, as to the remission of the entire punishment. So also before Baptism Cornelius and others like him receive grace and virtues through their faith in Christ and their desire for Baptism, implicit or explicit: but afterwards when baptized, they receive a yet greater fullness of grace and virtues. Hence in Psalm 22:2, “He hath brought me up on the water of refreshment,” a gloss says: “He has brought us up by an increase of virtue and good deeds in Baptism.”