The entire book of Hebrews is devoted to exhorting Jews not to return to their old ways of the Mosaic Law and thereby fall short of salvation when Jesus returns in glory. Right from the very beginning the writer has the Mosaic Law in mind and those Christians who were returning to it.
The book begins by demonstrating that Jesus is greater than the angels which is an allusion to the Mosaic Law (Heb 1:1- 2:13). The writer is brining up the issue of angels here because the Law was administered by angels and he is about to demonstrate that since Jesus is greater than Moses or the angels there is no need to have a fear that is one does not keep the Law they will not be saved. This may sound confusing so here are some passages which illustrate the relationship between the Law and angels:
"You who received the law by the administration of angels and did not keep it." (Acts 7:52).
"Why then the Law? It was added on account of transgressions, until the Seed might come to which the promise had been made, having been administered by angels in the hand of a mediator." (Galatians 3:30)
"For if the word spoken by angels was established and every transgression and disobedience received just recompense, how shall we escape, having neglected so great a salvation."
It is hard to know what these writers mean precisely but all we need to see is that they had a concept where the Law and angels were in some kind of relationship. It is for this reason that we see the writer to the Hebrews start off in this manner. He wants to illustrate how Jesus is above the angels so that he can demonstrate the superiority of Christianity over the Law. Note how the writer contrasts Jesus and the Gospel over angels and the Law right from the very beginning of chapter 2. In chapter 1, he was setting up for this argument over the Law which he will continue throughout the letter.
Notice in verse 2 how the writer says "we" referring to neglecting salvation. He is assuming that he is speaking to born again Christians as we shall further see throughout the letter.
The writer then proceeds to show that Jesus is greater than Moses (2:13 - 3:6; cf. John 1:17). Then he exhorts them to heed the voice of Christ through the Holy Spirit (3:7) and to not "depart from the living God" (3:12) as did the Israelites who rebelled in sin (3:18) against God in the wilderness (3:8-19). The message is clear. You cannot depart frmo the Living God if you are not already with the Living God. Those who do not stand firm but fall into rebellious disobedience will suffer the wrath of judgment. We are told plainly that we are partners with Christ with Christ in the heavenly calling only if we hold firmly until the end (3:1, 14). Also notice that these Israelites did not enter the rest of the promised land because of disobedience (3:18) and then the writer says they were unable to enter that rest because of unbelief (3:19). They did not enter because they were not united with faith (4:2) meaning they disobeyed what they had heard, or put another way, they did not believe what they had heard and disobeyed God. Therefore, they are not take careful heed that none fall short of entering that rest. The writer then exhorts them to persevere and enter that rest, unlike the unbelieving Israelites who rebelled against the will of God. Such an exhortation would make little sense if that is an impossibility as Calvinists claim. Indeed, this audience is reminded that God's judgment day is coming (4:12-13) and we are later told God will judge his people (10:30-31). The writer then moves on to portray Jesus Christ in the order of Melchizedek, one who is apart from the Mosaic Law and is greater than the Mosaic Law (4:14-5:10). The point he is trying to make here is that the way of Christ is greater than the way of the Mosaic Law. Christ has passed through the heavens (4:14) and is greater than all these things with all authority and power under his feet. Even Christ submitted himself to the Father, the One who could save him from death and he was heard because of his reverent submission (5:7) Then the writer again warns his audience not to fall away from grace (5:11-6:8). We only have one life of repentance and can only come to the cross once to be crucified with Christ (6:6; see Rom 6:3- 6). As he later says, it is destined for man to die once and after that face judgment (9:27). Those who produce "thorns and thistles" (i.e. the curse of sin, see Gen 3:17-19) are to be burned in the end (6:8; see 10:31; 12:29).. The writer then is more encourages his audience with a more hopeful outlook (6:9-20). He tells them that God will not overlook their work and their love for his sake and that all should show the same assurance of hope to the very end (6:11) and be imitators of those who through faith and patience will inherit the promises to come when Christ returns (6:12; cf. 9:28). God's promise is certain and is confirmed by oath (6:13-19) and we can have such hope as an anchor for our soul (6:19) just as Jesus our forerunner has entered that rest. Then the writer again turns to demonstrating that Christ is greater than the Law (7:1-10:19). Following this is a call to persevere. For if we willingly persist in sin after having been illuminated with the knowledge of the truth (i.e. conversion) there is no more sacrifice for sins (10:26; see 6:4-6). We cannot be "re-converted" and die with Christ and start all over again. Then they are severely warned that punishment will follow those who have spurned the Son of God in this way and have trampled the Spirit of grace underfoot (10:29-30). He warns them plainly and severely, that God will judge his people (10:30-31; see 1 Pet 1:17; 4:17). Rather, they are to recall the joy of their conversions when they were illuminated with truth and the sufferings they endured (10:32ff.). And they are then called to not abandon that first confidence (10:35) but to continue to endure until the end when Christ returns in glory (10:36-38) and not to shrink back and be lost but to continue their walk of faith in obedience to God and so be saved (10:39). Indeed, he goes on to describe what faith is, that whidch we do not yet see - the resurrection unto glory (cf. 11:17-18, 35). He gives examples of many who had not yet received their promise but endured to the end in hope of a "better resurrection", and "eternal city God has prepared for them" (11:16). It is quite plain he is exhorting them to hold on to their Christian faith until the end when Christ returns. Christ who is the author of our faith is also the finisher, he will come again and the promise will be fulfilled (12:1-2). He did not give up but suffered faithfully unto the end (12:3-7). Without holiness no one will see God (12:14). They are not to forfeit their inheritance like Esau. Such a warning is quite absurd if indeed it is impossible to do so as Calvinists claim. The Hebrews are not to refuse God and are told they will not escape his judgment at the end of time (12:27) any more than the Israelites who had done the same. The entire book is a pleading to hold on to their Christian walk of faith to not forfeit their inheritance as Esau did.. Excursus: Hebrews 6:4-8 and 10:26-39 Many Protestants are confused by the language of Hebrews 6:4-6. Here it appears to Armenian minded Protestants that that if one apostasizes he has not chance of recovery. This is quite a naive view of the Christian concept of repentance. In the entire book of Hebrews the writer is exhorting these Christians to hold on to their walk of faith. What the writer is conveying at Heb 6:4-6 is that we cannot be born again again. We only have one shot at the life of repentance. We cannot go to the cross and die with Christ again re-crucifying him (cf. Rom 6:2-6; Gal 2:20). It is impossible to be brought back to a second conversion event. We must continue steadfastly in the repentant life that we now have. Same idea at Hebrew 10:26ff. Calvinists try to pretend that these are people who heard the truth but were not regenerated. This is quite impossible because the writer discusses "renewing" repentance. One cannot renew something which he has not already had. Hebrews 10:26ff clarifies this inner illumination.