2Pe 2:21

2 Peter 2:20 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.

2 Peter 2:21 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.

2 Peter 2:22 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.

Though this passage is often used to prove that eternal security is not true, it actually says nothing about losing one's salvation. The context is false teachers who promote damnable heresies and deny the Lord (v. 1). It should be obvious that it is not saved men who are the focus on this passage, but hypocrites and deceivers. Any interpretation which says these are saved men who lose their salvation flies in the face of the context. The fact that "the latter end is worse with them than the beginning" and "it had been better for them not to have known the way of righteousness" does not imply that they were saved and now are lost. They were dogs and pigs who were unchanged (v. 22). The fact that they return to their wickedness proves that they were never regenerate. When the context is taken into account, there really is no problem in this passage in regard to the doctrine of eternal security.

Way of Life Encyclopedia

I agree with Bro Cloud that this passage is speaking of false teachers. Peter is definitely not speaking of salvation here.