But concerning the usefulness and healthiness of penance, so that we may accomplish what we have instituted: if, already despairing of health, you add sins to sins, as it is written: "The sinner, when he comes to the depths of evil, despises"; do not despise, do not despair; even from the depths cry out to the Lord and say to Him: "Out of the depths I have cried to You, O Lord; Lord, hear my voice. Let Your ears be attentive to the voice of my supplication. If You, Lord, should mark iniquities, O Lord, who could stand? For with You there is forgiveness." From such a depth the Ninevites cried out, and they found this propitiation; and it is easier to annul the prophecy’s threat than the humbling of penance. Maybe you say here: but I have already been baptized in Christ, by whom all my past sins have been forgiven; I have become very vile by repeating my ways, and like a dog horrible to the eyes of God, I have returned to my vomit. Where shall I go from His spirit? And where shall I flee from His presence? Where, brother, unless by repenting to His mercy, whom you had despised by sinning? For no one rightly flees from Him except to Him, from His severity to His goodness. For what place will receive you fleeing, where His presence will not find you? If you ascend into heaven, He is there: if you descend into hell, He is present. Therefore take your wings directly, and live in the hope at the farthest part of this age: for His hand will certainly lead you, and His right hand will hold you. For whatever you do, whatever sins you commit; you are still in this life, from which God would entirely take you away if He did not want to heal you. Why then do you not realize that the patience of God is leading you to repentance? For the one who did not persuade you by calling so that you would not depart, is calling you to return by sparing you.
Consider King David: certainly, he also had already received the sacraments of that time, he had certainly already been circumcised, which our fathers had for Baptism. For to this the Apostle says that holy Abraham received the sign of righteousness of the faith. He had already been anointed with the venerable anointing, which prefigured the royal priesthood of the Church. Meanwhile, having suddenly become guilty of both adultery and murder, he did not cry out in vain from such an immense and abrupt depth of sin, repenting to the Lord, saying: "Turn Your face away from my sins, and blot out all my iniquities." Indeed, for what merit except that he also says: "I acknowledge my iniquity, and my sin is always before me?" What then did he offer to the Lord to propitiate Him? “For if you wanted sacrifice,” he says, “I would have given it; You do not delight in burnt offerings. The sacrifice to God is a broken spirit; a contrite and humble heart, O God, You will not despise.” So he not only devoutly offered, but by saying this he showed what ought to be offered. For it is not enough to change habits for the better and to turn away from evil deeds; unless also for those things that have been done, satisfaction is made to God through the pain of penance, through the groan of humility, through the sacrifice of a contrite heart, with alms cooperating. For the merciful are blessed, because God will have mercy on them.
For it is not said that we should only abstain from sins: "But also," he says, “pray to the Lord for past sins, that they may be forgiven to you.” And Peter was already faithful, already in Christ, and had baptized others. Therefore, consider Peter, presuming, accused, fearing, wounded, weeping, healed. Even after the coming of the Holy Spirit from heaven, a certain Simon wanted to buy the same Holy Spirit with money, thinking of the most wicked and impious trade, already baptized in Christ: and yet he received the advice of penance from Peter himself. The Apostle Paul also says, who was surely sending letters to the faithful: "Lest when I come again, my God will humble me among you, and I shall weep for many who have sinned before and have not repented of the uncleanness and fornication and lewdness which they have committed." So we are surrounded both by precepts of doing right and by examples not only of those doing right, but also of those repenting to receive the salvation that had been lost through sinning. But suppose it is uncertain whether God will forgive. What does one lose who prays to God, who did not doubt to lose salvation when offending God? For who is certain that even the emperor will forgive? Yet money is spent, seas are crossed, the uncertainties of storms are faced; and almost to avoid death, death itself is endured. Then supplication is made through men to a man: these things are surely done without doubt, though it is uncertain to what end they will come. And yet the keys of the Church are more certain than the hearts of kings: with these keys whatever is loosed on earth is also promised to be loosed in heaven. And much more honorable is the humility with which one humbles himself to the Church of God: and a lesser labor is imposed, and without any danger of temporal death, eternal death is avoided.