the dog has returned to his vomit
2 Peter 2:22 Barnes
But it is happened unto them according to the true proverb - The meaning of the proverbs here quoted is, that they have returned to their former vile manner of life. Under all the appearances of reformation, still their evil nature remained, as really as that of the dog or the swine, and that nature finally prevailed. There was no thorough internal change, any more than there is in the swine when it is washed, or in the dog. This passage, therefore, would seem to demonstrate that there never had been any real change of heart, and of course there had been no falling away from true religion. It should not, therefore, he quoted to prove that true Christians may fall from grace and perish. The dog and the swine had never been anything else than the dog and the swine, and these persons had never been anything else than sinners.
The dog is turned to his own vomit again - That is, to eat it up. The passage would seem to imply, that whatever pains should be taken to change the habits of the dog, he would return to them again. The quotation here is from Pro 26:11; “As a dog returneth to his vomit, so a feel returneth to his folly.” A similar proverb is found in the Rabbinical writers. Of the truth of the disgusting fact here affirmed of the dog, there can be no doubt. Phaedrus (Fab. 27.) states a fact still more offensive respecting its habits. In the view of the Orientals, the dog was reckoned among the most vile and disgusting of all animals. Compare Deut 23:18; 1Sa 17:43; 2Sa 3:8; 2Sa 9:8; 2Sa 16:9; Mat 7:6; Php 3:2. See also Horace, II. Epis. 1, 26:
Vixisset canis immundus, vel amica luto sus.
On the use of this proverb, see Wetstein, in loc.
And the sow that was washed ... - This proverb is not found in the Old Testament, but it was common in the Rabbinical writings, and is found in the Greek classics. See Wetstein, in loc. Its meaning is plain, and of the truth of what is affirmed no one can have any doubt. No matter how clean the swine is made by washing, this would not prevent it, in the slightest degree, from rolling in filth again. It will act out its real nature. So it is with the sinner. No external reformation will certainly prevent his returning to his former habits; and when he does return, we can only say that he is acting according to his real nature - a nature which has never been changed, any more than the nature of the dog or the swine. On the characteristics of the persons referred to in this chapter, 2 Pet 2:9-19, see the introduction, Section 3.
This passage is often quoted to prove “the possibility of falling from grace, and from a very high degree of it too.” But it is one of the last passages in the Bible that should be adduced to prove that doctrine. The true point of this passage is to show that the persons referred to never “were changed;” that whatever external reformation might have occurred, their nature remained the same; and that when they apostatized from their outward profession, they merely acted out their nature, and showed that in fact there had been “no” real change. This passage will prove - what there are abundant facts to confirm - that persons may reform externally, and then return again to their former corrupt habits; it can never be made to prove that one true Christian will fall away and perish. It will also prove that we should rely on no mere external reformation, no outward cleansing, as certain evidence of piety. Thousands who have been externally reformed have ultimately shown that they. had no religion, and there is nothing in mere outward reformation that can suit us for heaven. God looks upon the heart; and it is only the religion that has its seat there, that can secure our final salvation.