Let us draw near with a true heart in full assurance of faith, having our hearts sprinkled from an evil conscience, and our bodies washed with pure water. Let us hold fast the profession of our faith without wavering; (for he is faithful that promised

And let us consider one another to provoke unto love and to good works: Not forsaking the assembling of ourselves together, as the manner of some is; but exhorting one another: and so much the more, as ye see the day approaching.
For if we sin wilfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins, But a certain fearful looking for of judgment and fiery indignation, which shall devour the adversaries. He that despised Moses’ law died without mercy under two or three witnesses: Of how much sorer punishment, suppose ye, shall he be thought worthy, who hath trodden under foot the Son of God, and hath counted the blood of the covenant, wherewith he was sanctified, an unholy thing, and hath done despite unto the Spirit of grace? For we know him that hath said, Vengeance belongeth unto me, I will recompense, saith the Lord. And again, The Lord shall judge his people. It is a fearful thing to fall into the hands of the living God. … Now the just shall live by faith: but if any man draw back, my soul shall have no pleasure in him. But we are not of them who draw back unto perdition; but of them that believe to the saving of the soul. (Hebrews 10:22-39 KJV)
St. Paul states that apostasy nullifies The effect of Christ’s sacrifice. You can be “truly regenerate” and fall from grace. He says, “ye have need of patience, that, after ye have done the will of God, ye might receive the promise.” He also says that “the just shall live by faith” (from Habakkuk 2:4), which does not mean that the just will necessarily exhibit faith, but that faith is necessary for the just to live. Thus, he continues, “if any man draw back, my soul shall have no pleasure in him.” There is no doubt that this passage concerns the truly regenerate because Paul explicitly states he is speaking about the man who is sanctified by the blood of the covenant (i.e. by the blood of Christ).
The usual objection is that, yes Paul is treating this issue as if it were a real possibility, but it’s actually still an impossibility. Say it is so. Presumably Paul is writing to real people (the Jews) about a real problem (judaizing and apostasy). If this passage is written off as an impossibility, then the letter ceases to be a true exhortation and becomes mere boasting over those wicked reprobates (which he elsewhere says “is excluded”). He says, “But we are not of them who draw back unto perdition; but of them that believe to the saving of the soul.” If this is a statement of absolute certitude that none of them could ever fall away, then his letter was pointless since his whole purpose is warning about the danger of apostasy. The more sensible interpretation is that this last verse is a statement of confidence similar to when you tell someone about to compete in a contest, “you’re going to win today.” It is a friendly encouragement even though losing is always a possibility.