Apostates are those who deny the faith by making the grace of God without effect . They went out from us because they were not of us.
2Peter 1:20 Knowing this first, that no prophecy of the scripture is of any private interpretation ....... (personal commentary)
Heresy defines the private interpretations as commentaries of one sect or denomination that makes them different than another.. The word sect/denomination come from the Greek word heresy.
Eastons bible dictionary Sect, heresy (Gr. hairesis, usually rendered "heresy", Acts 24:14; 1 Chr.11:19; Gal. 5:20, etc.), meaning properly "a choice," then "a chosen manner of life," and then "a religious party," as the"sect" of the Sadducees (Acts 5:17), of the Pharisees (15:5),the Nazarenes, i.e., Christians (24:5). It afterwards came to be used in a bad sense, of those holding pernicious error, divergent forms of belief (2 Pet. 2:1; Gal. 5:20).
The apostate Jews who resisted all thing written in the law and the fathers (sola scriptura) accused Paul a previous member formally under a law of the fathers, of heresy..
Act 24:5 For we have found this man a pestilent fellow, and a mover of sedition among all the Jews throughout the world, and a ringleader of the sect (heresy)of the Nazarenes:
Act 24:14 But this I confess unto thee, that after the way which they call heresy, so worship I the God of my fathers, believing all things which are written in the law and in the prophets
There are damnable heresies by which we can judge another and offer them the gospel. They deny the grace of God by the oral traditions of the fathers making all things written in the law and the fathers without effect. Those who be the apostate s denying the faith of Christ in exchange for doctrines of men.
2Peter 2:1 But there were false prophets also among the people, even as there shall be false teachers among you, who privily shall bring in damnable heresies, even denying the Lord that bought them, and bring upon themselves swift destruction.
They would be the ones that are hoping they will be found with a righteousness of their own after some work they have done. Again denying the grace of God that bought them.