16 Let us then, beloved, bearing these things in mind, be humbled, and feel thankful to those who are in debt to us. For they become to us, if we command ourselves, an occasion of obtaining most abundant pardon; and giving a little, we shall receive much. Why then exact with violence, it being meet, though the other were minded to pay, for you of your accord to excuse him, that you may receive the whole of God? But now you do all things, and art violent, and contentious, to have none of your debts forgiven you; and while you are thinking to do despite unto your neighbor, you are thrusting the sword into yourself, so increasing your punishment in hell: whereas if you will show a little self-command here, you make your own accounts easy. For indeed God therefore wills us to take the lead in that kind of bounty, that He may take occasion to repay us with increase.
As many therefore as stand indebted to you, either for money, or for trespasses, let them all go free, and require of God the recompense of such your magnanimity. For so long as they continue indebted to you, you can not have God your debtor. But if you let them go free, you will be able to detain your God, and to require of Him the recompense of so great self-restraint in bountiful measure. For suppose a man had come up and seeing you arresting your debtor, had called upon you to let him go free, and transfer to himself your account with the other: he would not choose to be unfair after such remission, seeing he had passed the whole demand to himself: how then shall God fail to repay us manifold, yea, ten thousand fold, when for His commandment's sake, if any be indebted to us, we urge no complaint against them, great or small, but let them go exempt from all liability? Let us not then think of the temporary pleasure that springs up in us by exacting of our debtors, but of the loss, rather, how great! Which we shall thereby sustain hereafter, grievously injuring ourselves in the things which are eternal. Rising accordingly above all, let us forgive those who must give account to us, both their debts and their offenses; that we may make our own accounts prove indulgent, and that what we could not reach by all virtue besides, this we may obtain by not bearing malice against our neighbors; and thus enjoy the eternal blessings, by the grace and love towards man of our Lord Jesus Christ, to whom be glory and might now and always, even forever and ever. Amen.
Source: Homilies on the Gospel of St. Matthew (New Advent)