Several individuals misunderstand Hebrews 6 and 10 and a host of other scriptures regarding eternal security. However, what most fail to realize is the church – the visible church to whom the writer of Hebrews was addressing his letter – contains both the elect and non-elect, both lost and saved, just like Israel did in the OT. The non-elect can be partakers of the Holy Spirit – but just not in the same way as the elect do. One of the tell tell signs that this is whom the writer of Hebrews is exhorting is the use of the term “babe” (nepios) in Hebrews 5:13. There are different types of babes – those that have been born (saved) and those that are lost (compare, Job 3:16, still-born, though one may in a way say they came closer to salvation then those that have never experience the Gospel, as their lives were in some way effected by the Holy Spirit, i.e. covenant children, et. al.).

Many people think that Hebrews 6:4-6 teaches that a person can lose his salvation, and then that he can never regain it. In reality, even though this passage talks about partaking of the Holy Spirit and tasting of the heavenly gift, it is not talking about people who are saved. As Hebrews 6:9 says, "Even though we speak like this, dear friends, we are confident of better things in your case—things that accompany salvation" (not sure how your quoted scholars missed that verse?) That is, even though the author speaks in this threatening way, he means his words to apply to those in the church who are not saved and who despise Christ, not to those who are saved. Of those who are saved, he expects "better things ... things that accompany salvation."

Note:

• Christians are predestined not just to initial salvation but to eternal salvation (Acts 13:47-48; Rom. 8:28-30; 9:18-24; Eph. 1:3-14; 1 Thess. 5:9-10).
• Christ's death secured salvation for those for whom he died (Heb. 9:11-15).
• Justification (being declared righteous and forgiven by God) cannot be lost or revoked (Rom. 5:8-10,15-19; 8:1-4,9-11,29-30; Heb. 9:11-12).
• The saved/elect are given to Christ as a permanent possession (John 6:35-40; 10:25-29).
• The saved/elect are kept secure in Christ by God (John 6:35-40; 10:25-29; Rom. 8:28-39; 1 Cor. 1:4-9; 2 Cor. 4:13-14; Eph. 1:13-14; 4:30; Phil. 1:6; 3:20-21; Col. 3:3-4; 1 Thess. 5:23-24; 1 Pet. 1:3-5; 1 John 2:19; 5:4; Jude 1,24-25).
• Eternal life begins at conversion, and by definition may never end (John 3:14-16,36; 4:14; 5:24; 6:35-40,44-58; 10:25-29; 17:1-3; 20:31; Rom. 6:22-23; 1 Tim. 6:12; Heb. 9:15; 1 John 5:11-13,20).
• God is sovereign in salvation, his will must be accomplished, and he wills the perseverance of the saints (Job 42:1-2; Isa. 14:24,27; 46:8-11; Matt. 18:12-14; John 6:35-40).

Reformed and Always Reforming,