For when they speak great swelling words of emptiness, they allure through the lusts of the flesh, through lewdness, the ones who have actually escaped from those who live in error. While they promise them liberty, they themselves are slaves of corruption; for by whom a person is overcome, by him also he is brought into bondage. For if, after they have escaped the pollutions of the world through the knowledge of the Lord and Savior Jesus Christ, they are again entangled in them and overcome, the latter end is worse for them than the beginning. For it would have been better for them not to have known the way of righteousness, than having known it, to turn from the holy commandment delivered to them. But it has happened to them according to the true proverb: “A dog returns to his own vomit,” and, “a sow, having washed, to her wallowing in the mire.” (II Peter 2:18-22 NKJV)
When Peter talks about those who have escaped the pollution of the world through the knowledge of Jesus Christ, and then becoming entangled again with that which they had escaped, he is not talking about one losing their salvation. He is talking about those whose "committment" to Christ is not genuine to begin with. They have a head knowledge of Jesus Christ but not a heart knowledge. In applying the Proverbs mentioned at the end of this passage, he is in effect saying that their nature never was changed by God. Therefore, it is no surprise that they became entangled again with the world and with false teachers. Their end will be worse than if they had not known the way of righteousness. Why? Because those who have correct knowledge and reject it have a greater condemnation than those who are ignorant of the truth.