"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, And have tasted the good word of God, and the powers of the world to come, 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 6:4-6 KJV)
OK, here's my 'take' on this. The book of Hebrews is one of the Epistles of Paul, the man whose mission it was to evangelize the gentiles. So what's he up to in preaching to the Hebrews? They had had numerous prophets down through the ages; why should he have felt that they needed another one so close on after the appearance of Jesus to them?
Look at Heb. 3: 1-3: Paul is addressing people to whom he now feels bound, as if in brotherhood, and he says to them, "Holy brethren, partakers of the heavenly calling" ... God just sent you a prophet more worthy even than Moses whom you all reverence etc etc. Paul goes on in chapter 4 to unbraid the Jews for not having taken Jesus' message to heart: "the word preached did not profit them, not being mixed with faith in them that heard it" (Heb. 4:2). Chapter 6:1-3 adds some new things to be done by the Hebrews, who already had a very long list of things to be done (not to wear clothing made of two fibres, not to eat the flesh of various animals, to make sin offerings and burnt offerings and so on and so on); these new things to be done would have seemed strange to them: baptism, laying on of hands, resurrection of the dead...
And NOW Paul says to them in Heb.6:4-6 (I freely paraphrase here): 'listen, you've had umpteen prophets before this, you KNOW what you are to do, you're God's CHOSEN people, you've had warnings and signs and wonders (none of these blessings did the gentiles have)--now for Christ's sake, get on with it! This is your last warning, and if you screw it up this time, there's nothing left for you.'
I think it is about apostasy, for the whole of the Hebrew nation. Make any sense?