2 But since we need to practise all the divine laws alike, and more especially that which bids us consider no man as an enemy, nor retain resentment long, but immediately to be reconciled; suffer us today to discourse to you concerning this commandment. For as it is not to be imagined that the fornicator and the blasphemer can partake of the sacred Table, so it is impossible that he who has an enemy, and bears malice, can enjoy the holy Communion. And this with good reason. For a man when he has committed fornication, or adultery, at the same time that he has accomplished his lust, has also completed the sin; and should he be willing by watchful living to recover from that fall, he may afterwards, by manifesting great penitence, obtain some relief. But he who is resentful works the same iniquity every day, and never brings it to an end. In the former case the deed is over, and the sin completed; but here the sin is perpetrated every day. What excuse can we then have, I ask, for delivering ourselves willingly to such an evil monster? How can you ask your Lord to be mild and merciful to you, when you have been so hard and unforgiving to your fellow-servant?
Source: Homilies on the Statues (New Advent)