Letter 1
But now hear how this has actually occurred in real instances. Amongst the Corinthians some man of mark committed a sin such as was not named even among the Gentiles. This man was a believer and belonged to the household of Christ; and some say that he was actually a member of the priesthood. What then? Did Paul cut him off from the communion of those who were in the way of salvation. By no means: for he himself it is who rebukes the Corinthians countless times, backwards and forwards, because they did not bring the man to a state of repentance: but, desiring to prove to us that there is no sin which cannot be healed, he said again concerning the man who had transgressed more grievously than the Gentiles: “Deliver such an one to Satan for destruction of the flesh that his spirit may be saved in the day of the Lord Jesus Christ.” Now this was prior to repentance: but after he had repented “Sufficient,” said he, “for such an one is this punishment which was inflicted by the many” and he charged them by a letter to console the man again, and to welcome his repentance, so that he should not be got the better of by Satan. Moreover when the whole Galatian people fell after having believed, and wrought miracles, and endured many trials for the sake of their faith in Christ he sets them up again. For that they had done miracles he testified when he said: “He therefore that supplies to you the Spirit and works miracles among you:” and that they endured many contests for the sake of the faith, he also testified when he says: “Have ye suffered so many things in vain if it be indeed in vain.” Nevertheless after making so great an advance they committed sin sufficient to estrange them from Christ concerning which he declares saying: “Behold, I Paul tell you, that if you be circumcised, Christ will profit you nothing:” and again “ye who would be justified by the law are fallen away from grace:” and yet even after so great a lapse he welcomes them saying “my little children of whom I am in travail again until Christ be formed in you” showing that after extreme perversion it is possible for Christ to be formed again in us: for He does not desire the death of a sinner, but rather that he should be convened and live.
Source: Two Letters to Theodore After His Fall (New Advent)