Titus 3:10

But as many as separate from the Church, and give heed to such old wives' fables as these, are truly self-condemned; and these men Paul commands us, "after a first and second admonition, to avoid.".
"Such was the horror which the apostles and their disciples had against holding even verbal communication with any corrupters of the truth; as Paul also says, "A man that is an heretic, after the first and second admonition, reject; knowing that he that is such is subverted, and sinneth, being condemned of himself."

On this point, however, we dwell no longer, since it is the same Paul who, in his Epistle to the Galatians, counts "heresies" among "the sins of the flesh," who also intimates to Titus, that "a man who is a heretic" must be "rejected after the first admonition," on the ground that "he that is such is perverted, and committeth sin, as a self-condemned man." Indeed, in almost every epistle, when enjoining on us (the duty) of avoiding false doctrines, he sharply condemns heresies.

That we must not speak with heretics. To Titus: "A man that is an heretic, after one rebuke avoid; knowing that one of such sort is perverted, and sinneth, and is by his own self condemned." Of this same thing in the Epistle of John: "They went out from among us, but they were not of us; for if they had been of us, they would doubtless have remained with us." Also in the second to Timothy: "Their word doth creep as a canker."

But for the rest, let our most beloved brethren firmly decline, and avoid the words and conversations of those whose word creeps onwards like a cancer; as the apostle says, "Evil communications corrupt good manners." And again: "A man that is an heretic, after one admonition, reject: knowing that he that is such is subverted, and sinneth, being condemned of himself." And the Holy Spirit speaks by Solomon, saying, "A perverse man carrieth perdition in his mouth; and in his lips he hideth a fire." Also again, he warneth us, and says, "Hedge in thy ears with thorns, and hearken not to a wicked tongue." And again: "A wicked doer giveth heed to the tongue of the unjust; but a righteous man does not listen to lying lips." And although I know that our brotherhood there, assuredly fortified by your foresight, and besides sufficiently cautious by their own vigilance, cannot be taken nor deceived by the poisons of heretics, and that the teachings and precepts of God prevail with them only in proportion as the fear of God is in them; yet, even although needlessly, either my solicitude or my love persuaded me to write these things to you, that no commerce should be entered into with such; that no banquets nor conferences be entertained with the wicked; but that we should be as much separated from them, as they are deserters from the Church; because it is written, "If he shall neglect to hear the Church, let him be unto thee as a heathen man and a publican." And the blessed apostle not only warns, but also commands us to withdraw from such. "We command you," he says, "in the name of Jesus Christ our Lord, that ye withdraw yourselves from every brother that walketh disorderly, and not after the tradition which he received of us." There can be no fellowship between faith and I faithlessness. He who is not with Christ, who is an adversary of Christ, who is hostile to His unity and peace, cannot be associated with us. If they come with prayers and atonements, let them be heard; if they heap together curses and threats, let them be rejected.

Perhaps even thus being put to shame by the bad odor of their names, they [the heretics] may be enabled to grasp the depth of impiety into which they have fallen. It would be within our rights not to answer them at all, according to the apostolic advice: “One who is heretical, after a first and a second admonition refuse, knowing that such a one is perverted and sins, being self-condemned.” This is even more the case, in that the prophet says about such men: “The fool shall utter foolishness, and his heart shall imagine vain things.” But since, like their leader, they too go about like lions seeking whom among the simple they shall devour, we are compelled to write in reply to your piety, that the brethren being once again instructed by your admonition may still further reprove the vain teaching of those men.

If he who has been corrected for his first sins and has been deemed worthy of pardon again falls, he prepares for himself a more wrathful judgment. He who after the first and second admonition remains in his fault should be reported to the superior, that perhaps he may be ashamed when further rebuked. But, if he does not even in this case correct himself, he must be cut off from the rest as a cause of scandal and be looked upon as a heathen and a publican.

This monster’s cavern [of heresies], your sacred Majesty, is thick laid (as seafaring men do say it is) with hidden lairs, and all the surrounding neighborhood, where the rocks of unbelief echo to the howling of her black dogs, we must pass by with ears stopped up. For it is written: “Hedge your ears about with thorns” and again: “Beware of dogs. Beware of evil workers"; and yet again: “One who is a heretic, avoid after the first reproof knowing that such a one is fallen and is in sin, being condemned of his own judgment.” So then, like prudent pilots, let us set the sails of our faith for the course wherein we may pass by most safely and again follow the coasts of the Scriptures.

How then does he elsewhere say, "If God peradventure will give them repentance" (2 Tim. ii. 25); but here, "A man that is an heretic after the first and second admonition reject, knowing that he that is such is subverted and sinneth, being condemned of himself"? In the former passage he speaks of the correction of those of whom he had hope, and who had simply made opposition. But when he is known and manifest to all, why dost thou contend in vain? why dost thou beat the air? What means, "being condemned of himself"? Because he cannot say that no one has told him, no one admonished him; since therefore after admonition he continues the same, he is self-condemned.

What then? dost thou command him to stop the mouths of gainsayers, if he must pass them by when they are doing everything to their own destruction? He means that he should not do it principally for their advantage, for being once perverted in their minds, they would not profit by it. But if they injured others, it behooved him to withstand and contend with them; and manfully await them, but if thou art reduced to necessity, seeing them destroying others, be not silent, but stop their mouths, from regard to those whom they would destroy. It is not indeed possible for a zealous man of upright life to abstain from contention, but so do as I have said. For the evil arises from idleness and a vain philosophy, that one should be occupied about words only. For it is a great injury to be uttering a superfluity of words, when one ought to be teaching, or praying, or giving thanks. For it is not right to be sparing of our money but not sparing of our words; we ought rather to spare words than our money, and not to give ourselves up to all sorts of persons.

What means, "that they be careful to maintain good works"? That they wait not for those who are in want to come to them, but that they seek out those who need their assistance. Thus the considerate man shows his concern, and with great zeal will he perform this duty. For in doing good actions, it is not those who receive the kindness that are benefited, so much as those who do it that make gain and profit, for it gives them confidence towards God. But in the other case, there is no end of contention: therefore he calls the heretic incorrigible. For as to neglect those for whom there is a hope of conversion is the part of slothfulness, so to bestow pains upon those who are diseased past remedy is the extreme of folly and madness; for we render them more bold.

Avoid a heretical man after one and a second admonition, knowing that such a one is subverted, and sins, being condemned by himself. The name of heresy is stated in the Epistle to the Corinthians: For there must be also heresies: that they also, which are approved, may be made manifest among you (1 Cor. 11:19). And among the works of the flesh, it is listed in the Epistle to the Galatians: Now the works of the flesh are manifest, which are these; Adultery, fornication, uncleanness, lasciviousness, Idolatry, witchcraft, hatred, variance, emulations, wrath, strife, seditions, heresies, Envyings, murders, drunkenness, revellings, and such like: of the which I tell you before, as I have also told you in time past, that they which do such things shall not inherit the kingdom of God. (Gal. 5:19-21). It should be carefully observed in these things, that just as the other vices, which are counted among the works of the flesh, exclude us ((Al. are excluded)) from the kingdom of God: so too heresies take away the kingdom of God from us; and it does not matter how someone is excluded from the kingdom. But what is even more remarkable seems to be that thing in the Acts of the Apostles, our faith in Christ, and Ecclesiastical discipline, already being labeled as heresy by perverse men at that time. For the Jews say to the Apostle Paul, "Neither have we received letters from you from Judea ((Al. from you... from Judea)), nor has anyone coming from the brethren reported or spoken any evil of you. But we ask to hear from you what your views are; for it is well known to us about this heresy, because everywhere it is contradicted (Acts 28:21,22)." And though the name of the heresy of Miletus is not mentioned, yet they are designated by the labours of Paul, in his address to the presbyters of the Church, 'I know that after my departure grievous wolves shall enter in among you, not sparing the flock; and of your own selves shall men arise speaking perverse things, to draw away disciples after them' (Acts 20:29-30). These remarks are made in passing, as it were, where elsewhere also heresy is spoken of. The name itself must now be fully examined. In Greek, heresy means an election, that is, everyone chooses for himself that which he thinks best. The philosophers, too, Stoics, Peripatetics, Academics, Epicureans, are called followers of this or that sect. It is needless to go through each one separately, and to enumerate the various dogmas of Marcion, Valentinus, Apelles, Ebion, Montanus, and Manichæus, seeing it is very easy for everyone to know what are the particular errors advocated by each individual. Arius and Eunomius, and the author of the new heresy, would that they were not so well known, perhaps they would have deceived fewer! Therefore, avoid a heretic after the first admonition, or as is better expressed in Greek, νουθεσία, which signifies warning or teaching rather than reproach; which is approved in Latin copies sometimes cited with approval by Pope Athanasius, to the effect that people who are wronged are not sufficient to be informed or warned once or twice, but that the second time they should be given instruction, and that every word should stay in the mouth of two or three witnesses. But why he should be avoided after the first and second admonitions, he gives the reasons, namely, that he is perverted and sins, being condemned by himself. For he who, having been corrected once or twice, does not wish to be corrected after hearing his mistake, is considered to be in error by the corrector: and on the contrary, when preparing for arguments and disputes with words, he wishes to make profit from the one from whom he learnt. Therefore, it is said to be condemned by oneself: because fornication, adultery, murder, and other vices are repelled by priests of the Church. But heretics bring judgment upon themselves, departing from the Church by their own choice: which departure seems to be a condemnation of their own conscience. They think that heresy differs from schism in that heresy has perverse doctrine, while schism separates from the Church due to episcopal dissension, which can be understood to some extent at the beginning. However, no schism does not invent some heresy for itself, so that it may appear to have departed from the Church correctly.

Warn a heretical man once or twice, and then reject him; knowing that such a person is perverted and sins, being self-condemned.

— [OECUMENIUS] And elsewhere Paul says, "May God not grant them repentance." (2 Tim. 2:25) How then does he here order to cease? There he speaks about correction for those who have hope; here, however, about those suffering incurable diseases. [end of the excerpt by Oecumenius R f. 300r] —

being self-condemned. For Paul has no defense to offer, saying, "No one told me; no one advised me." Being self-condemned means either being without defense or being condemned by oneself and one's own conscience.