POSSIBLY IT IS IMPOSSIBLE
Hebrews 6:4-6 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.
The writer of this epistle directs the teaching found in the lesson text to Hebrew Christians, who had once obeyed the first principles of the doctrine of Christ, and were added to His body - the church of Christ. These Christians were the ones spoken of in the last verses of the previous chapter as those that ought to be teachers, but, due to the lack of further edification through the study of God's will, had remained babes in Christ. These same Christians were told, in the first three verses of this chapter, to leave behind these basic foundational principles of the doctrine of Christ, (and) ...go on to perfection.
The writer now gives us scriptural proof that eternal salvation is not assured for enlightened Christians. They can, and sometimes do, abandon the faith that brought them into the body of Christ, fall away, and become guilty of apostasy. These enlightened Christians had originally tasted of the heavenly gift. That is, they heard about this gift offered by God, through the preaching of the gospel message of Jesus Christ. They understood it, and they accepted it as the most wonderful gift ever offered to mankind - the hope of eternal salvation.
Enlightened Christians, through obedience, are also made partakers of the Holy Ghost. Jesus told His apostles that God would send the Holy Ghost, and He shall teach you all things, ...whatsoever I have said unto you (John 14:26). The New Covenant doctrine, the gospel of Christ, was sent to mankind though the Holy Ghost. It is the sword of the Spirit, which is the word of God,that enables all Christians to stand against the wiles of the devil (See Eph. 6:11-17). The apostle, Paul, told the Christians at Rome, But ye are not in the flesh, but in the Spirit, if so be that the Spirit of God dwell in you (Rom. 8:9a). When we diligently study God's Holy Spirit inspired word, the Bible, we are filled with the Spirit of God and accepting, believing, and obeying that HolyWord, we become partakersof the Holy Ghost.
Verse 5, of the lesson text, tells us that the good word of God is spiritual food for the soul. Christians are to feast sumptuously on it. By inspiration the Psalmist confirmed this when he wrote, How sweet are thy words unto my taste! Yea, sweeter than honey to my mouth (Psalm 119:103)! The lesson text further describes the good word of God as the powers of the world to come. The power of God was revealed by His holy word, and it was revealed in the world to come. The time, referred to here, is the same as the "age to come," or "the last days" or "the last times" which were common phrases used by the Jewish nation when referring to the coming of the Messiah - the Christian Dispensation.
The lesson text tells us that it is possible for enlightened Christians - those that have tasted of the heavenly gift, those that were made partakers of the Holy Ghost, and those that have tasted the good word of God;to fall away from the love of Christ, return to their old sinful ways, and be eternally lost. We know that God is not willing that any should perish, but that all should come to repentance (2 Peter 3:9). However, the sixth verse of the lesson text warns that it is possible for children of God to fall away to a degree that it is not possible for them to repent. We know that godly sorrow worketh repentance to salvation (2 Cor. 7:10), therefore, we must assume that, a falling away from which there is no repentance, is when one is beyond godly sorrow.
When is repentance impossible? It is when one has fallen away from the love of God, to the extent that they become hostile to the Son of God, likened to the rebellious, cruel-hearted Jews that rejected Jesus as the Messiah, had Him crucified on the cross of Calvary. It is true that apostate Christians cannot literally crucify Christ again. However, they can oppose His gospel message of salvation, condemn it, speak evil against it, and lead others into sin and lose the hope of salvation. For these unremorseful, degenerate Christians that have fallen away from righteousness, possibly it is impossible for them to come to repentance, be forgiven, return to God through Jesus Christ, and have the hope of eternal salvation.