8 “Forgive us our debts, as we forgive our debtors.” Is this necessary except in this life? For in the other we shall have no debts. For what are debts, but sins? See, you are on the point of being baptized, then all your sins will be blotted out, none whatever will remain. Whatever evil you have ever done, in deed, or word, or desire, or thought, all will be blotted out. And yet if in the life which is after Baptism there were security from sin, we should not learn such a prayer as this, “Forgive us our debts.” Only let us by all means do what comes next, “As we forgive our debtors.” Do ye then who are about to enter in to receive a plenary and entire remission of your debts, do ye above all things see that you have nothing in your hearts against any other, so as to come forth from Baptism secure, as it were free and discharged of all debts, and then begin to purpose to avenge yourselves on your enemies, who in time past have done you wrong. Forgive, as you are forgiven. God can do no one wrong, and yet He forgives who owes nothing. How then ought he to forgive, who is himself forgiven, when He forgives all, who owes nothing that can be forgiven Him?
Source: Sermons on Selected Lessons of the New Testament (New Advent)