16 I see some ground on which I may comfort not some few only, but the multitude of Christians: and I know that you are longing to hear it. Christ has said, “Forgive, that you may be forgiven.” And what do ye say in the Prayer which we have now been discussing? “Forgive us our debts, as we also forgive our debtors.” So, Lord, forgive, as we forgive. This you say, “O Father, which art in heaven, so forgive our debts, as we also forgive our debtors.” For this ye ought to do, and if you do it not, you will perish.
When your enemy asks pardon, at once forgive him. And is this much for you to do? Though it were much for you to love your enemy when violent against you, is it much to love a man who is a supplicant before you? What have you to say? He was before violent, and then you hated him. I had rather you had not hated him even then: I had rather then when you were suffering from his violence, you had remembered the Lord, saying, “Father, forgive them, for they know not what they do.” I would have then much wished that even at that time when your enemy was violent against you, you had had regard to the Lord your God speaking thus.
But perhaps you will say, He did it, but then He did it as being the Lord, as the Christ, as the Son of God, as the Only-Begotten, as the Word made flesh. But what can I, an infirm and sinful man, do? If your Lord be too high an example for you, turn your thoughts upon your fellow-servant. The holy Stephen was being stoned, and as they stoned him, on bended knees did he pray for his enemies, and say, “Lord, lay not this sin to their charge.” They were casting stones, not asking pardon, yet did he pray for them.
I would you were like him; reach forth. Why are you for ever trailing your heart along the earth? Hear, “Lift up your heart,” reach forward, love your enemies. If you can not love him in his violence, love him at least when he asks pardon. Love the man who says to you, “Brother, I have sinned, forgive me.” If you then forgive him not, I say not merely, that you dost blot this prayer out of your heart, but you shall be blotted yourself out of the book of God.
Source: Sermons on Selected Lessons of the New Testament (New Advent)