But anyway, the bible has a stern warning for those who sin after baptism:
Heb 10:26 For if we sin willfully after we have received the knowledge of the truth, there no longer remains a sacrifice for sins,
Heb 10:27 but a certain fearful expectation of judgment, and fiery indignation which will devour the adversaries.
Heb 10:28 Anyone who has rejected Moses’ law dies without mercy on
the testimony of two or three witnesses.
Heb 10:29 Of how much worse punishment, do you suppose, will he be thought worthy who has trampled the Son of God underfoot, counted the blood of the covenant by which he was sanctified a common thing, and insulted the Spirit of grace?
In regards to Hebrews 10:26, To "sin willfully" in the Greek carries the idea of deliberate intention that is habitual, which stems from rejecting Christ deliberately. This is CONTINUOUS ACTION - A MATTER OF PRACTICE. Now we don't walk along our daily life and "accidentally" fall into a pit called sin. We exercise our will but, the use of the participle clearly shows a CONTINUOUS ACTION. The
unrighteous practice sin - (1 Corinthians 6:9-10; Galatians 5:19-21)
not the righteous, who are born of God - (1 Corinthians 6:11; 1 John 3:9).
The reference to "the blood of the covenant that sanctified him" in verse 29 "on the surface" appears to be referring to a Christian, but this overlooks the fact that the word translated "sanctified" (which is a term often applied to Christians; is the verb form of the adjective "holy") which means "set apart," and doesn't necessarily refer to salvation. In 1 Corinthians 7:14, Paul uses it to specifically refer to non-Christians who are "sanctified" or "set apart" by their believing spouse.
(And by this Paul does not mean that they are saved). A non-Christian can be "set apart" from other non-Christians without experiencing salvation as Paul explained. So the word "sanctified" means to be "set apart." If the word "sanctified" simply meant saved, then you would have to say that the Sabbath was saved (Genesis 2:3), the tabernacle was saved (Exodus 29:43), the Lord was saved (Leviticus 10:3), the Father saved the Son (John 10:36) and many other things that do not line up with scripture.
In verse 39, the author sets up the contrast that makes it clear to me that he was referring to unbelievers, not saved people: But
we are not of those who draw back to perdition, but
of those who believe to the saving of the soul. Those who
draw back to perdition do not believe to the saving of the soul and those who
believe to the saving of the soul do not draw back to perdition.
So after considering the context, it seems most likely that "he was sanctified" should be understood in the sense of someone who had been "set apart" or identified as a participant in the Hebrew Christian community of believers, but who committs apostasy by renouncing his identification with the Hebrew Christian community of believers, by rejecting the "knowledge of the truth" that he had received, and by refusing to accept the work and person of Jesus Christ himself, thus giving evidence that his identification with these Hebrew Christians was superficial and in vain and that he was not a genuine believer.
If the word 'sanctified' in Hebrews 10:29 is used to describe saved people who lost their salvation, then we have a contradiction because the writer of Hebrews in verse 10 said
"sanctified through the offering of the body of Jesus Christ once for all" (Hebrews 10:10) and in verse 14, we read,
"perfected for all time those who are sanctified." (Hebrews 10:14) *Also, in Romans 8:30, we read - Moreover whom He predestined, these He also called; whom He called, these He also justified;
and whom He justified, these He also glorified. *ALL of them.