Knowing that he who is such is ruined He declares that man to be "ruined," as to whom there is no hope of repentance, because, if our labor could bring back any man to the right path, it should by no means be withheld. The metaphor is taken from a building, which is not merely decayed in some part, but completely demolished, so that it is incapable of being repaired. He next points out the sign of this ruin -- an evil conscience, when he says, that they who do not yield to admonitions are condemned by themselves; for, since they obstinately reject the truth, it is certain that they sin willfully and of their own accord, and therefore it would be of no advantage to admonish them. At the same time, we learn from Paul's words that we must not rashly or at random pronounce any man to be a heretic; for he says, "Knowing that he who is such is ruined." Let the bishop therefore beware lest, by indulging his passionate temper, he treat with excessive harshness, as a heretic, one whom he does not yet know to be such.

Knowing that he that is such is subverted - Literally, "is turned out;" or, "is changed," i. e., for the worse. He has gone from the right way, and therefore he should be rejected.
And sinneth, being condemned of himself - His own conscience condemns him. He will approve the sentence, for he knows that he is wrong; and his self-condemnation will be punishment sufficient. His own course, in attempting a division or schism in the church, shows him that it is right that he should be separated from the communion of Christians. He that attempts to rend the church, without a good reason, should himself be separated from it.

Is subverted - Is turned out of the way in which he may be saved, and consequently sinneth - enters into that way that leads to destruction.
Being condemned of himself - This refers to the Judaizing teacher, who maintained his party and opinions for filthy lucre's sake. He was conscious of his own insincerity; and that he proclaimed not his system from a conscientious love of truth, but from a desire to get his livelihood. Were the Church in all countries, whether established by law or unestablished, strictly scrutinized, multitudes of heretics of this kind would be found. And perhaps this is the only bad sense in which the word should be understood.

Knowing that he that is such is subverted,.... Or overturned and demolished; he is like an edifice, that is not only decaying, and falling, but is entirely everted, and pulled down; so that there is no hopes of a restoration or recovery; he is in a desperate condition, having opposed the person, or office, or sacrifice of Christ; having either trodden the Son of God underfoot, or counted his blood common, or done despite unto the spirit of grace; in either of which cases there is no more sacrifice for sin:
and sinneth; not practically, but doctrinally, and wilfully after he has received the knowledge of the truth; by denying the truth he received, in which he continues, notwithstanding the evidence of the word of God is against him; and; notwithstanding the arguments taken from it by the ministers of the Gospel, to convince him; and notwithstanding the admonitions of the church to recover him out of the snare of the devil:
being condemned of himself; not that an heretic is one that is convinced in his own conscience that he is in an error, and that that is a truth which he opposes; and yet he obstinately persists in the one, and continues to set himself against the other; for then, none but an hypocrite, that conceals his true sentiment, can be an heretic; nor can any man be known to be one unless he accuses himself; since no man can know the heart of another; and it would be impracticable in a church to deal with heretics, or reject and excommunicate them: but either the meaning is, that he is such an one, who by his own practice has condemned himself; for whereas he has separated himself not only from the faith of the church, but from the church itself; by so doing he practically condemns himself, or judges himself unworthy of the communion of the church, and so justifies the church in their rejection and exclusion of him: or rather, an heretic is one who having professed Christianity, and received the Scriptures as the only rule of faith and practice, and still professes to abide by the same, and that all doctrine is to be tried by them, and to be approved or condemned as that agrees or disagrees with them, stands condemned by those Scriptures, which he himself allows to be the rule of decision and determination; and so may be said to be self-condemned.

is . . . subverted--"is become perverse."
condemned of himself--He cannot say, no one told him better: continuing the same after frequent admonition, he is self-condemned. "He sinneth" wilfully against knowledge.

Such an one is perverted - In his heart, at least. And sinneth, being self - condemned - Being convinced in his own conscience that he acts wrong.