John Calvin Commentary Titus 3:11

"knowing that such a one is perverted, and sinneth, being self-condemned." — Titus 3:11 (ASV)

Knowing that he who is such is ruined. He declares that person to be “ruined,” for whom there is no hope of repentance, because if our labor could bring anyone back 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 those 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 by their own choice, and therefore it would be useless to admonish them.

At the same time, we learn from Paul’s words that we must not rashly or randomly pronounce anyone to be a heretic; for he says, Knowing that he who is such is ruined. The bishop, therefore, should take care that, by indulging his passionate temper, he does not treat with excessive harshness, as a heretic, someone whom he does not yet know to be such.