On the Unity of the Catholic Church 17

Yet let not the excessive and abrupt faithlessness of many move or disturb us; rather let it strengthen our faith by the truth of what was foretold. As some have begun to be such because these things were foretold beforehand, so let the other brothers beware of such people, because these things too were foretold beforehand, as the Lord instructs us and says: "But you, beware; see, I have told you all things beforehand." Avoid such men, I beg you, and keep away from your side and your ears their deadly conversations as the contagion of death, as it is written: "Hedge your ears with thorns, and do not listen to a wicked tongue." And again: "Evil talk corrupts good character." The Lord teaches and warns that we must withdraw from such: "They are blind," he says, "leaders of the blind. But if the blind leads the blind, both will fall into the ditch." Whoever has been separated from the church must be turned from and shunned. Such a man is perverted and sins and is condemned by himself. Does he think he is with Christ who acts against the priests of Christ, who separates himself from the fellowship of his clergy and people? He bears arms against the church; he fights against God's arrangement. An enemy of the altar, a rebel against the sacrifice of Christ, faithless instead of faithful, sacrilegious instead of religious, a disobedient servant, an impious son, a hostile brother, despising the bishops and forsaking the priests of God, he dares to set up another altar, to make another prayer with unlawful words, to profane the truth of the Lord's offering by false sacrifices; not knowing that he who strives against God's ordinance is punished by divine chastisement for the audacity of his rashness.