23 I indeed desire, beloved brethren, and I equally endeavour and exhort, that if it be possible, none of the brethren should perish, and that our rejoicing Mother may enclose in her bosom the one body of a people at agreement. Yet if wholesome counsel cannot recall to the way of salvation certain leaders of schisms and originators of dissensions, who abide in blind and obstinate madness, yet do you others, if either taken in simplicity, or induced by error, or deceived by some craftiness of misleading cunning, loose yourselves from the nets of deceit, free your wandering steps from errors, acknowledge the straight way of the heavenly road.
The word of the witnessing apostle is: “We command you,” says he, “in the name of our Lord Jesus Christ, that you withdraw yourselves from all brethren that walk disorderly, and not after the tradition that they have received from us.” And again he says, “Let no man deceive you with vain words; for because of these things comes the wrath of God upon the children of disobedience. Be not therefore partakers with them.” We must withdraw, nay rather must flee, from those who fall away, lest, while any one is associated with those who walk wickedly, and goes on in ways of error and of sin, he himself also, wandering away from the path of the true road, should be found in like guilt.
God is one, and Christ is one, and His Church is one, and the faith is one, and the people is joined into a substantial unity of body by the cement of concord. Unity cannot be severed; nor can one body be separated by a division of its structure, nor torn into pieces, with its entrails wrenched asunder by laceration. Whatever has proceeded from the womb cannot live and breathe in its detached condition, but loses the substance of health.
Source: The Treatises of Cyprian (New Advent)