They promise them freedom, but they themselves are slaves of corruption. For whatever overcomes a person, to that he is enslaved.
19. While they promise them liberty. He shews their inconsistency, that they falsely promised liberty, while they themselves served sin, and were in the worst bondage; for no one can give what he has not. This reason, however, does not seem to be sufficiently valid, because it sometimes happens that wicked men, and wholly unacquainted with Christ, preach usefully concerning the benefits and blessings of Christ.
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
While they promise them liberty,.... Not Christian liberty, which lies in a freedom from sin, its dominion, guilt, and condemnation, and in serving God with liberty, cheerfulness, and without fear; but a sinful carnal liberty, a liberty from the law of God, from obedience to it as a rule of walk and conversation, and from the laws of men, from subjection to the civil magistrate...