Are all of our sins —past, present, and future— forgiven once and for all when we become Christians? Not according to the Bible or the early Catholic Church Fathers. Scripture nowhere states that our future sins are forgiven; instead, it teaches us to pray, "And forgive us our debts, as we also have forgiven our debtors" (Matt. 6:12).
The means by which God forgives sins after baptism is confession: "If we confess our sins, he is faithful and just, and will forgive our sins and cleanse us from all unrighteousness" (1 John 1:9). Minor or venial sins can be confessed directly to God, but for grave or mortal sins, which crush the spiritual life out of the soul, God has instituted a different means for obtaining forgiveness—the sacrament known popularly as confession, penance, or reconciliation.
This sacrament is rooted in the mission God gave to Christ in his capacity as the Son of man on earth to go and forgive sins (cf. Matt. 9:6). Thus, the crowds who witnessed this new power "glorified God, who had given such authority to men" (Matt. 9:8; note the plural "men"). After his resurrection, Jesus passed on his mission to forgive sins to his ministers, telling them, "As the Father has sent me, even so I send you. . . . Receive the Holy Spirit. If you forgive the sins of any, they are forgiven; if you retain the sins of any, they are retained" (John 20:21–23).
Since it is not possible to confess all of our many daily faults, we know that sacramental reconciliation is required only for grave or mortal sins—but it is required, or Christ would not have commanded it.
Penances also tended to be performed before rather than after absolution, and they were much more strict than those of today (ten years’ penance for abortion, for example, was common in the early Church).
Of special significance is their recognition that confession and absolution must be received by a sinner before receiving Holy Communion, for "[w]hoever . . . eats the bread or drinks the cup of the Lord in an unworthy manner will be guilty of profaning the body and blood of the Lord" (1 Cor. 11:27).