17 These people are springs without water and mists driven by a storm. Blackest darkness is reserved for them. 18 For they mouth empty, boastful words and, by appealing to the lustful desires of the flesh, they entice people who are just escaping from those who live in error. 19 They promise them freedom, while they themselves are slaves of depravity—for “people are slaves to whatever has mastered them.” 20 If they have escaped the corruption of the world by knowing our Lord and Savior Jesus Christ and are again entangled in it and are overcome, they are worse off at the end than they were at the beginning. 21 It would have been better for them not to have known the way of righteousness, than to have known it and then to turn their backs on the sacred command that was passed on to them. 22 Of them the proverbs are true: “A dog returns to its vomit,” and, “A sow that is washed returns to her wallowing in the mud.”
Peter continues to point out the error in the false teachers. The false teaching he highlights today is that they taught that since we are free in Christ, we are free to do what we want to do. Since we are no longer under the law, the law doesn't matter anymore. He calls this living according to the lustful desires of the flesh. Worse yet, they were enticing newer believers that didn't know any better, and were very vulnerable to returning to a previous lifestyle.
But the problem with this so called "freedom" was that it was not really freedom at all. By going back to their sinful desires they were enslaved again. And in fact, he infers also that if someone having tasted freedom through the knowledge of Christ returns to their previous lifestyle they are worse off than before. Why? Because when we lived under the slavery of the flesh before we knew Christ, we were really just acting the only way we knew. But now that we know Jesus, to go back to an old lifestyle is a willful rejection of what Jesus has done for us by nailing our sin to the cross. When we sin without batting an eye after we have been saved, we are taking the gift of grace and throwing back in Jesus' face. We are not counting the cost of our sin, and what He paid to set us free.
It is as if someone gave you a million dollars to pay off your debt and then right after he did, you went and lost a million more in Vegas. Not only would you have the same debt, but know you would feel horrible toward your benefactor. You could barely look him in the eye. If this is true in a worldly sense, how much more true when the Son of God gave his life to set you free from sin and you went right back into it. Peter likens it to a dog returning to his vomit, or a pig after having been washed clean, returning to the muddy pig pen.
We can see why these teachers were so dangerous, because they cheapened the grace of God. And every time we willfully go back to our old sinful nature, we so the same thing. Of course we are not perfect and make mistakes, but this is more the willful returning to a old lifestyle of sin. Where one says I am free so I will just do whatever I want, after all I am forgiven. You can see how absurd this is when we look at it this way, and yet we will all continue to battle against our sinful nature until Jesus calls us home.
The bottom line is that Jesus has given us true freedom. Freedom from slavery to sin and the power of the devil. In our freedom we can serve God and love others and pursue our true purpose in life. We can find fulfillment in who we have been called to be. We have also been given the power of the Spirit, who directs us in the way we should go according to God's Word. As we live by the Spirit, we are promised to have freedom from the sinful nature. In fact, the last fruit of the Spirit is "self control". Go Figure!