4 For it is impossible for those who were once enlightened, and have tasted the heavenly gift, and have become partakers of the Holy Spirit,
5 and have tasted the good word of God and the powers of the age to come,
6 if they fall away, to renew them again to repentance, since they crucify again for themselves the Son of God, and put Him to an open shame.
7 For the earth which drinks in the rain that often comes upon it, and bears herbs useful for those by whom it is cultivated, receives blessing from God;
8 but if it bears thorns and briers, it is rejected and near to being cursed, whose end is to be burned.
Those who think the warning in these verses is hypothetical — Stam, KJV Commentary, Wuest
Those who think the warning is addressed to Jews who were never saved — Ironside, Vine, Pink, Wuest
Those who think the warning was to Jews saved under the Kingdom who could lose their salvation — McLean
After all, they were baptized by Christ with the heavenly gift of the Holy Spirit starting at Pentecost and continuing until Israel fell. They were the ones who had tasted the good word of God and the powers of the world to come, which happens to be the focus of the book of Hebrews according to Hebrews 2:5. These Hebrews are the ones with the God-given ability to walk in God’s statues (Ezekiel 36:27) because the law of God is written in their hearts (Jeremiah 31:31-34; Hebrews 8:8-10) and they have no need that any man teach them (1 John 2:27).
For the Holy Ghost-baptized Hebrew people to fall away from what their Messiah had provided them would be to put Christ to an open shame and would constitute blasphemy on the level of blaspheming the Holy Spirit Himself. — McLean, page 87
once (v.4) = once for all — without need of repetition
enlightened (v.4) — the truth was made clear
partakers (v.4) = hold with — the tense states a mere fact, not a finished act with continuing results
powers (v.5) — used of miracles
fall away (v.6) = to deviate from the right path, to turn aside — tense is “if they fell away”
to themselves (v.6) — so far as they are concerned
The apostate crucifies Christ on his own account by virtually confirming the judgment of the actual crucifiers, declaring that he, too, has made a trial of Jesus and found Him no true Messiah but a deceiver and therefore worthy of death. — Wuest, page 118