Apostasy in Judaism is the rejection of Judaism and possible conversion to another religion by a Jew. The term apostasy is derived from ancient Greek, meaning rebellious. Hebrews 6:4-6 states the impossibility of repentance for those who fall away after receiving a blessing from God. "It is impossible for those who have once been enlightened, who have tasted the heavenly gift, who have shared in the Holy Spirit, who have tasted the goodness of the word of God and the powers of the coming age, and who have fallen away, to be brought back to repentance. To their loss, they are crucifying the Son of God all over again and subjecting him to public disgrace."
He starts by saying that it is impossible, a very concrete, unmovable word. The word impossible is put in a position of emphasis. The writer does not say this is merely difficult but impossible meaning, without possibility. He uses the same emphasis in verse 18 when referring to lying and in verse 4 when referring to animal sacrifice as being impossible to take away sin. In chapter 11, the writer refers to the impossibility of pleasing God without faith. All these references use the exact meaning of the word impossible as immovable, having no possibility at all. Secondly, the writer says that those who were once enlightened have tasted the heavenly gift, have become partakers of the Holy Spirit, and have tasted the good word of God and the powers of the age to come; he is speaking of people with a seaming myriad of Spiritual experience. However, is this the experience of salvation or the spiritual experience of something just short of salvation? He says that they tasted the good word of God; this implies that the gospel was preached to them, that they probably experienced the goodness of God’s word and saw its goodness at work in them, as people who have experienced God’s supernatural power but are just short of salvation.
Can someone have great spiritual experiences and still fall away? The Pharisees in the NT is a good example of this. These men did many religious things but were not saved or submitted to God. Therefore, it may safely be said that from a human perspective, they had all appearances of salvation; nevertheless, from the perspective of God’s perfect wisdom, they were not saved. However, this passage is best understood in Hebrews 6:1-2, explaining that if they retreat back to Judaism, all the repentance in the world will do them no good. Returning from Christianity to the safe ideas and customs of their former religious experience is to forsake Jesus and crucify Him again. This is especially true for these ancient Christians from a Jewish background who would return again to animal sacrifice for atonement that would deny the total work of Jesus for them on the cross.
In chapter 10:26, the writer speaks of willful sinning. This is the frighting idea of consciously and deliberately rejecting Christ. Like in chapter six, to know God’s way, hear it preached, study it, count oneself among the faithful, and then turn away is to become an apostate is difficult and fighting to understand. The writer describes the apostate as one who does not sin out of ignorance; he is not carried away by some momentary temptation or is too weak to resist. The willful apostate in Hebrews sins because of an established way of thinking and acting, which he has no desire to give up. On the other hand, the true believer lapses into sin and loses temporary fellowship with God. However, he will eventually return to God in repentance because his heavenly Father will ruthlessly chase after him and convict him until he can’t escape. The resolute apostate will continue to sin deliberately, willingly, and with abandon. John says, "No one who is born of God will continue to sin because God’s seed remains in them; they cannot sin because they have been born of God. (1 John 4:9).
Finally, in Hebrews 6:9, The Hebrew writer says, "We are confident of better things concerning you." Though he first spoke very severely, the writer to the Hebrews was confident His readers would continue on with Jesus. After his strong warning, I believe these encouraging words should not be understood to mean that the warnings in the previous verses are not serious or that the writer warned of impossible consequences. If anything, verse nine shows how badly these floundering Hebrew Christians needed encouragement. Their spiritual danger was not so much out of a calculated rebellion but more because of a depressing discouragement. They needed warning but also needed encouragement.