In Book 2 of "Treatise on the Merits and Forgiveness of Sins, and on the Baptism of Infants," Augustine appears to argue the necessity of penance to remedy sin. In chapter 3 he writes, "The Lord, therefore, foreseeing that such would be our character, was pleased to provide and endow with efficacious virtue certain healthful remedies against the guild and bonds even of sins committed after baptism,--for instance, the works of mercy,--as when he says: 'Forgive, and ye shall be forgiven; give, and it shall be given unto you.'"
In chapter 4 he writes, "Such, however, as yield consent to it for the commission of unlawful deeds, it holds as guilty; and unless, through the medicine of repentance, and through works of mercy, by the intercession in our behalf of the heavenly High Priest, they be healed, it conducts us to the second death and utter condemnation."
Later in the chapter he writes, "When, therefore, we have by an unlawful inclination of our will yielded consent to these lusts of the flesh, we say, with a view to the cure of this fault, "Forgive us our debts;" and we at the same time apply the remedy of a work of mercy, in that we add, 'As we forgive our debtors.'"
How should this be interpreted?