3. This passage presents to the readers a hypothetical situation that could not possible become a reality.
#3. Hebrews 6:4-6 is a stern warning of the real peril of rejecting one’s faith in Christ.
If you look at the context of these scriptures it is clear that the topic that the author is discussing is not a warning about what will happen if you reject Christ, but instead is an incouragement to move on to deeper understandings of the faith.
Hebrews 5:12-6:6
12. For when for the time ye ought to be teachers, ye have need that one teach you again which be the first principles of the oracles of God; and are become such as have need of milk, and not of strong meat.
13. For every one that useth milk is unskilful in the word of righteousness: for he is a babe.
14. But strong meat belongeth to them that are of full age, even those who by reason of use have their senses exercised to discern both good and evil.
1.Therefore leaving the principles of the doctrine of Christ, let us go on unto perfection; not laying again the foundation of repentance from dead works, and of faith toward God, 2. Of the doctrine of baptisms, and of laying on of hands, and of resurrection of the dead, and of eternal judgment.
3. And this will we do, if God permit.
4. For it is impossible for those who were once enlightened, and have tasted of the heavenly gift, and were made partakers of the Holy Ghost,
5. And have tasted the good word of God, and the powers of the world to come,
6. If they shall fall away, to renew them again unto repentance; seeing they crucify to themselves the Son of God afresh, and put him to an open shame.
Hebrews 5:12-14 describes the difference between those who eat "milk" and those who eat "meat". He tells them that while they are currently drinking milk they should instead be chewing on a steak (metaphoricly speaking of course). After saying this, the author goes on to say in 6:1-3 that as a result they shouldn't be worrying about the fundimentals of salvation and baptism, but that they should move on into "perfection" . At which point the author writes 6:4-6.
Since verse 4 sarts out with "For" it is a clear indicator that what follows is an explaination of why the earlier is true. In this case the author is in essence saying that you don't need to worry about those fundimentals in your own life, they have already had their effect on you and if you were to fall away, it wouldn't matter because they couldn't be done again for you. So move on! Eat some meat!
Also, why can't God use hypothetical situations to reveal imortant and very real truths? In fact there is presidence in the Bible for these kinds of hypothetical situations. I Corinthians 13:2 states: "And though I have the gift of prophecy, and understand all mysteries, and all knowledge; and though I have all faith, so that I could remove mountains, and have not charity, I am nothing"
There is no man (save Jesus) that understands all mysteries, has all knowledge, and has all faith. This is a hypothetical situation that teaches a very real truth (that love is very important) just as Hebrews 6:4-6 is a hypothetical situation that teaches a very real truth, once we are saved we should stop worrying about our salvation and chew on something tougher.
May God bless and guide you.