Lets let The Bible Talk:-
2 Peter 2:20-22
Certainly if after escaping from the defilements of the world by an accurate knowledge of the Lord and Savior Jesus Christ, they get involved again with these very things and are overcome, their final state has become worse for them than the first.
21 It would have been better for them not to have accurately known the path of righteousness than after knowing it to turn away from the holy commandment they had received. 22 What the true proverb says has happened to them: “The dog has returned to its own vomit, and the sow that was bathed to rolling in the mire.”
Gone back into Satan's world and left The Truth about Jesus.
The Metaphor of a "dog" and "sow" (pig) were unclean animals in the Jews so as peter is form a Jewish back ground he uses them to show that the Christian that 'turns away' and goes back to Satan's world is now become unclean and no longer fit for God to use, he/she is again defilied,' an outcast, gone back to serving Satan, thus useless unless he repents from his bad actions.
BT
Paul had to speak this way so as to not discriminate against anyone in church attendance. He spoke to all as though they were saved. But we see from 1 Cor 5 and 6 that he makes it clear to them / all of us that nobody in a mortal type sin must be confident of their salvation.
I don't like to argue this subject as I prefer us teaching the importance of examining ourselves daily. Mankind 101 = we assume the best of ourselves. But in all truthfulness it is simply insanity to suggest God can make the mistake of washing someone clean only to give them back to satan. We make mistakes, God does not. Once God has washed someone clean, they are clean indeed.
If you persist, please answer this question. Knowing that partiality is evil and that Peter grasped as we should that God is impartial Acts 10:34. So, how is God impartial with the criminal next to Jesus on the cross? One decision and a few hours on earth, then on to eternal bliss. When us, who get saved are used by God to further His kingdom at our risk of eternal damnation. Makes no sense. If you or anyone truly believed you can lose your salvation, you should desire to go and be a martyr for God asap.