11 “And forgive us our debts, as we forgive our debtors.” Touching this petition again we need no explanation, that it is for ourselves that we pray. For we beg that our debts may be forgiven us. For debtors are we, not in money, but in sins. You are saying perchance at this moment, And you too. We answer, Yes, we too. What, you Holy Bishops, are you debtors? Yes, we are debtors too. What you! My Lord. Be it far from you, do not yourself this wrong. I do myself no wrong, but I say the truth; we are debtors: “If we say we have no sin, we deceive ourselves, and the truth is not in us.” We have been baptized, and yet are we debtors.
Not that anything then remained, which was not remitted to us in Baptism, but because in our lives we are contracting ever what needs daily forgiveness. They who are baptized, and immediately depart out of this life, come up from the font without any debt; without any debt they leave the world. But they who are baptized and are still kept in this life, contract defilements by reason of their mortal frailty, by which though the ship be not sunk, yet have they need of recourse to the pump.
For otherwise little by little will that enter in by which the whole ship will be sunk. And to offer this prayer, is to have recourse to the pump. But we ought not only to pray, but to do alms also, because when the pump is used to prevent the ship from sinking, both the voices and hands are at work. Now we are at work with our voices, when we say, “Forgive us our debts, as we also forgive our debtors.” And we are at work with our hands when we do this, “Break your bread to the hungry, and bring the houseless poor into your house. Shut up alms in the heart of a poor man, and it shall intercede for you unto the Lord.”
Source: Sermons on Selected Lessons of the New Testament (New Advent)