Dr. Van Impe concurs with Lewis Sperry Chafer’s explanation of Hebrews 10:26-29 which some have used, along with verses in Hebrews 6, to wrongly teach the possibility of a born-again believer turning from Christ and consequently losing his salvation. Dr. Chafer writes in his Systematic Theology:

The peculiar character of the hortatory passages in the Hebrews Epistle is evident in this context. The writer is concerned about conditions then obtaining–little appreciated today. This plight was well described by James when he said to Paul as Paul returned to Jerusalem from years of Gentile ministry: “Thou seest, brother, how many thousands (literally, myriads–cf.Heb. 12:22; Rev. 5:11) of Jews, there are which believe; and they are all zealous of the law” (Acts 21:20). The writer to the Hebrews is addressing Jews who are interested in Christ and have, in a sense, believed; but not to the extent of receiving the death of Christ as the fulfillment and termination of Jewish sacrifices. The confusion of law and grace is always distressing, but no such situation as this has ever existed before or since. These circumstances account for these exhortations which were addressed to Jews who, whatever their religious experience might have been, were yet unsaved. There are seven “if’s” in this epistle which condition this type of Jews. The writer, of course, being a Jew, employs, as a recognition of Jewish unity, the pronoun we. These conditional passages are: “How shall we escape, if we neglect so great salvation?” (2:3); “Whose house are we if we hold fast the confidence and the rejoicing of the hope firm unto the end” (3~6); “We are made partakers of Christ, if we hold the beginning of our confidence steadfast unto the end” (3:14); “This will we do, if God permit.  For it is impossible for those who were once enlightened,…if they shall fall away, to renew them again unto repentance” (6:3-4, 6); “If we sin willfully after that we have received the knowledge of the truth, there remaineth no more sacrifice for sins” (10:26); “If any man draw back, my soul shall have no pleasure in him” (10:38); “Much more shall we escape, if we turn away from him that speaketh from heaven” (12:25).

This particular passage (Hebrews 10:26-29) is parenthetical. It is not a continuation of the theme set forth in the preceding verse. Those enjoined in verse 25 are believers, while those addressed in this text are hesitating Jews who demur concerning a right relation to Christ. Sinning willfully means that form of sin which is recognized in the Old Testament as not being a sin of ignorance.  Willful sin calls for divine forgiveness based on sacrificial blood. This warning reminds the Jew of the new situation in which the Mosaic sacrifices no longer avail, and it is therefore a choice between Christ’s sacrifice or judgment. To sin now, after Christ has died, is more serious. Sin is no longer an insult to the character and government of God alone, but it becomes also a direct rejection of Christ. In so far as Christ has died for men, they are classified, or set apart, as those for whom He died, which is sanctification according to its true meaning. No New Testament Scripture describes more clearly the sinfulness of sin in this age than this; but it is not a warning to Christians, nor does it imply their insecurity.

It will be recalled that there is a peculiar blindness upon Israel respecting the gospel. Of this blindness Christ said: “For judgment I am come into this world, that they which see not might see; and that they which see might be made blind” (John 9:39), and this blindness was predicted by Isaiah: “And he said, Go, and tell this people, Hear ye indeed, but understand not; and see ye indeed, but perceive not.  Make the heart of this people fat, and make their ears heavy, and shut their eyes, lest they see with their eyes, and hear with their ears, and understand with their heart, and convert, and be healed” (Isaiah 6:9-10). The Apostle refers to this again in II Corinthians 3:14-16. It is not strange, therefore, that there should be difficulty and hesitation on the part of unregenerate Jews.