Of them the proverbs are true: “A dog returns to its vomit,” and, “A sow that is washed goes back to her wallowing in the mud.”
22. But it has happened unto them. As the example disturbs many, when men who had submitted to the obedience of Christ, rush headlong into vices without fear or shame, the Apostle, in order to remove the offense, says that this happens through their own fault, and that because they are pigs and dogs. It hence follows that no part of the sin can be ascribed to the gospel.
The apostle's design being to warn us of, and arm us against, seducers, he now returns to discourse more particularly of them, and give us an account of their character and conduct, which abundantly justifies the righteous Judge of the world in reserving them in an especial manner for the most severe and heavy doom, as Cain is taken under special protection that he might be kept for uncommon vengeance.
Commenting on 2 Peter 2:10-22
But it is happened unto them, according to the true proverb,.... Which is true, both in fact and in the application of it, and which lies in the Scriptures of truth, at least the first part of it, Pro 26:11.