Well, Thanks, Hopeful.Yes, according to Paul.
You posted the verse .
Heb 6:4
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,
Heb 6:5
And have tasted the good word of God, and the powers of the world to come,
Heb 6:6
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.
This writer of Hebrews is a long way deeper into things than the crowd around Jesus in John 6.