Nicene and Post-Nicene Fathers, Vol. III:
Doctrinal Treatises of St. Augustin: Section 15

15. “Forgiveness of sins.” Ye have [this article of] the Creed perfectly in you when ye receive Baptism. Let none say, “I have done this or that sin: perchance that is not forgiven me.” What hast thou done? How great a sin hast thou done? Name any heinous thing thou hast committed, heavy, horrible, which thou shudderest even to think of: have done what thou wilt: hast thou killed Christ? There is not than that deed any worse, because also than Christ there is nothing better. What a dreadful thing is it to kill Christ! Yet the Jews killed Him, and many afterwards believed on Him and drank His blood: they are forgiven the sin which they committed. When ye have been baptized, hold fast a good life in the commandments of God, that ye may guard your Baptism even unto the end. I do not tell you that ye will live here without sin; but they are venial, without which this life is not. For the sake of all sins was Baptism provided; for the sake of light sins, without which we cannot be, was prayer provided. 1803 What hath p. 375 the Prayer? “Forgive us our debts, as we also forgive our debtors.” 1804 Once for all we have washing in Baptism, every day we have washing in prayer. Only, do not commit those things for which ye must needs be separated from Christ’s body: which be far from you! For those whom ye have seen doing penance, 1805 have committed heinous things, either adulteries or some enormous crimes: for these they do penance. Because if theirs had been light sins, to blot out these daily prayer would suffice.

Footnotes

Inventus

Matt. 6.12. [See R.V.]

“Agere pœnitentiam.”