Expositor's Bible Commentary Commentary 2 Peter 2:22

"It has happened unto them according to the true proverb, The dog turning to his own vomit again, and the sow that had washed to wallowing in the mire." — 2 Peter 2:22 (ASV)

Peter concludes his strong denunciation of the false teachers by citing two proverbs. The first is a biblical one (Proverbs 26:11); the second is extrabiblical. Both dogs and pigs were considered vile by the Jews. Jesus also used the designations “dogs” and “pigs” in speaking of those opposed to God and his Word (cf. Matthew 7:6). So the false teachers are unclean and return to the pagan corruption. The “dog [that] returns to its vomit” or the sow that “is washed” portrays the person who has a religious profession or outward change without a regenerating inner change that affects his or her nature. Such persons soon revert to their true nature.