Peter makes use of the proverbs to underscore his point about the false teachers and their behaviour. The first proverb is drawn from Proverbs 26:11 whereas the second one likely comes from a common observation of the nature of pigs. At the time, dogs were not seen as pets but despised and miserable animals who roamed wild in the street. To call someone a dog was a great insult (1 Samuel 17:43; Psalm 22:16, Psalm 22:20; Philippians 3:2) and those so described were considered evil (Matthew 7:6; Revelation 22:15). In the Jewish context, pigs were also considered unclean (Leviticus 11:7; Deuteronomy 14:8).1 The animals in the proverb are both dirty and disgusting in the Jewish mind, similar to the immoral life of pagan society.2 Both proverbs thus indicate a return to what is unclean, calling to one who returns to an animal.3
22 What the true proverb says has happened to them: “The dog returns to its own vomit, and the sow, after washing herself, returns to wallow in the mire.”