The Enchiridion 74
74 God Does Not Pardon the Sins of Those Who Do Not from the Heart Forgive Others PL 40, 267
Now, he who asks forgiveness of the man against whom he has sinned, being moved by his sin to ask forgiveness, cannot be counted an enemy in such a sense that it should be as difficult to love him now as it was when he was engaged in active hostility. And the man who does not from his heart forgive him who repents of his sin, and asks forgiveness, need not suppose that his own sins are forgiven of God. For the Truth cannot lie. And what reader or hearer of the Gospel can have failed to notice, that the same person who said, “I am the Truth,” taught us also this form of prayer; and in order to impress this particular petition deeply upon our minds, said, “For if ye forgive men their trespasses, your heavenly Father will also forgive you; but if ye forgive not men their trespasses, neither will your Father forgive your trespasses”? The man whom the thunder of this warning does not awaken is not asleep, but dead; and yet so powerful is that voice, that it can awaken even the dead.
Peccata non dimittenti non dimittuntur a Deo. Jam vero qui eum, in quem peccavit, hominem rogat, si peccato suo movetur ut roget, non est adhuc deputandus inimicus, ut eum diligere sit difficile, sicut difficile erat quando inimicitias exercebat. Quisquis autem roganti et peccati sui poenitenti non ex corde dimittit, nullo modo existimet a Domino sua peccata dimitti; quoniam mentiri veritas non potest. Quem vero lateat Evangelii auditorem sive lectorem, quis dixerit, Ego sum veritas ? Qui cum docuisset orationem, hanc in ea positam sententiam vehementer commendavit, dicens: Si enim dimiseritis hominibus peccata eorum, dimittet et vobis Pater vester coelestis peccata vestra. Si autem non dimiseritis hominibus, nec Pater vester dimittet peccata vestra . Ad tam magnum tonitruum qui non expergiscitur, non dormit, sed mortuus est: et tamen potens est ille etiam mortuos suscitare.