Jesus said to his disciples:  "I tell you, unless your righteousness surpasses that of the scribes and Pharisees, you will not enter into the Kingdom of heaven.
You have heard that it was said to your ancestors, 'You shall not kill; and whoever kills will be liable to judgment.'
But I say to you, whoever is angry with his brother will be liable to judgment, and whoever says to his brother, 'Raqa,' will be answerable to the Sanhedrin, and whoever says, 'You fool,' will be liable to fiery Gehenna.
Therefore, if you bring your gift to the altar, and there recall that your brother has anything against you,
leave your gift there at the altar, go first and be reconciled with your brother, and then come and offer your gift.
Settle with your opponent quickly while on the way to court with him. Otherwise your opponent will hand you over to the judge, and the judge will hand you over to the guard, and you will be thrown into prison.
Amen, I say to you, you will not be released until you have paid the last penny."

Gospel commentary

Blessed Columba Marmion (1858-1923), Abbot
The cenobitical society (Christ, the Ideal of the Monk, London: Sands & Co., 1934, pp. 78-79, rev.)

It may happen (…) that one may "excommunicate" oneself one's brethren. This may be done by failing in charity; by excluding someone, if not from one's heart, at least from the radiation of effective love. Again, one may "excommunicate" someone from the hearts of others by exciting them to distrust him. This is a sin so contrary to the Christian spirit that we should be especially on our guard against it and act in this manner with the greatest delicacy.

The cenobitical society is one, the cement that joins together its different members is charity. If that is diminished, the divine life also tends to be lowered in the social body. What, in fact, is the distinctive sign whereby the members of the Christian family are infallibly recognized, the sign given by Christ himself? It is mutual love (cf. Jn 13:35). It is the same for the monastic community, and the true mark of the protection of Christ Jesus over s religious community is the charity that reigns between its members. Woe to those who impair, in whatever manner it may be, this spirit of charity. In rending the robe of the Bride, they tear from their own soul the Christian sign excelling all others.

Christ is one; he tells us that what we do to the least of his brethren¬ — of his brethren — of good or evil, we do to himself. (cf. Mt 25:40, 45).