“Of them the proverbs are true: ‘A dog returns to his vomit,’ and, ‘A sow that is washed goes back to her wallowing in the mud.’”
Peter doesn’t hold back tearing into the false teachers and their ways. It is pretty clear that the specific teachers Peter has in mind here are propagating a license to sin. They misapply the hint of the Gospel they have heard, and promote the opposite of a correct response. They hear grace and forgiveness and see permission to satisfy lust and sin with abandon.
Licentiousness is an error, but it is generally recognized as false teaching today. That said, the other end of the spectrum is just as bad, not generally recognized as error, and fits the description as well.
Both licentiousness and legalism begin with a small understanding of the Gospel and end in obsession with sin. Legalism is just as obsessed with lust and sin as licentiousness, but it tries to find a way out through behavior and symbolism.
Correct teaching begins with a right understanding of sin and ends in an obsession with the Gospel. When we understand the extent of our rebellion and the sinfulness of our nature, the Gospel is correctly seen as the only hope to a situation that we can never overcome. And, the more we understand the extent of what Christ has done for us, the more our passions and behavior are changed by Him.
This is especially evident in today’s headlines. Prominent figures in the legalist branches of Christianity are being exposed as frauds. They preach detailed legalist approaches to sexual sin, but are being exposed as participants in the very sins that they claim to protect people from. Their system of belief and their practical applications of what they see as the Christian life expose an obsession with sex. Instead of a detailed list of acceptable behaviors intended to save people from sexual sin, they should be focused on the Gospel as the only source of liberation from the shackles of sin. Biblical teaching would have us be focused on and obsessed with Christ, not the sin from which He has freed us.