What does 2 Peter 2:20-22 mean?

20 For if after they have escaped the pollutions of the world through the knowledge of the Lord and Saviour Jesus Christ, they are again entangled therein, and overcome, the latter end is worse with them than the beginning. 21 For it had been better for them not to have known the way of righteousness, than, after they have known it, to turn from the holy commandment delivered unto them. 22 But it is happened unto them according to the true proverb, The dog is turned to his own vomit again; and the sow that was washed to her wallowing in the mire. (2 Peter 2:20-22 KJV)

Thomas Scott

Verses 20-22: If professed Christians, having escaped the outward pollutions of the world by the knowledge of Christ ( Note, 2Pe 1:3-4), were again by the artful seductions of false teachers, entangled in those polluting practices as if consistent with the service of Christ, and so overcome as habitually to indulge in their corrupt inclinations; their latter end, after they had learned thus to pervert the gospel, would be far worse than the beginning, when they sinned in ignorance, as they must have done violence to far clearer light and fuller conviction.

It would therefore have been better for such wretched heretics, hypocrites, or apostates if they had “never known the way of righteousness,” and the truths, promises, and precepts of Christianity, than, after all their instructions, convictions, and profession, to turn, in avowed disobedience, from the holy commandment, to repent of their sins, to believe in Christ, and to love and obey him; as this would leave them more deeply condemned and completely hardened. But it was not to be wondered at that teachers of this character made many proselytes; for it happened unto them according to the true proverb of Solomon (Note, Pr 26:11), and to another of similar import; the one of which hath been explained, and the other is too obvious to need explanation.

—[‘These two proverbs, of which the first is taken from Pr 26:11, and the second is common among the writers de re rustica, are very expressive of the folly of those men who return to those vices they had formerly renounced; and therefore the fathers apply them to Julian returning to that heathenism he had renounced in his baptism.’ Whitby. –Ed.]

—They are the two most disgusting and loathsome emblems which the whole animal race can suggest; and are adduced to illustrate the filthiness of those who, after convictions, professed repentance and reformation, returned back to wickedness, because their carnal hearts loved it. But if the power of God should change the swine into a sheep (the emblem of the regenerate, though it might be thrown into the mire, yet it could no longer wallow in it with delight, but must be most uncomfortable till cleansed from it. (Notes, Mt 12:43-45; Lu 11:14-26; Heb 6:4-8; 10:26-39)

—The difference between this chapter and the other parts of Peter’s epistles, in the style and manner, and its coincidence with that of Jude, have made several expositors suppose that both of them borrowed their language from some ancient book which is now lost; but of this, every reader must judge for himself.