Verses 7-13
Warning against unbelief (3:7-4:13)
The writer warns his disheartened Jewish readers with some reminders from Israel's experiences in the wilderness (see Exodus 17:1-7; Numbers 20:1-13; Psalms 95:7-11). Those experiences show that people who appear to be God's people may be so unbelieving, bitter and complaining, that they cannot enjoy the inheritance God has promised (7-11). They should resist the tendency to unbelief and stubbornness, by encouraging one another to maintain their faith with confidence to the end (12-15). They should bear in mind that many who shared in the deliverance from Egypt were refused entrance into the promised land because of their unbelief (16-19).
God's will was that the people of Israel, having been freed from bondage in Egypt, should find rest in Canaan, the land God promised them. In the same way God wants people everywhere to be freed from the bondage of sin and find rest in Jesus Christ. But, as with Israel, unbelief will exclude them from this promised rest (4:1-2). God's rest has been available from the time he created the world as a human dwelling place, but because of sin, people have not found this rest. It becomes theirs only through faith (3-5).
The Israelites who were disobedient under Moses did not reach the land or find the rest that God promised them. The Israelites who entered Canaan under Joshua were those of the generation that followed. However, long after the time of Joshua, David repeated God's promise of rest. This indicates that occupation of Canaan was not the complete fulfilment of God's promise (6-8; see Psalms 95:7-8). The real rest that God promises is salvation through faith. Just as God rested after his work of creation, so people will find true rest when they stop working to try to earn salvation and trust in what Christ has done for them (9-10; cf. Matthew 11:28).
People must make every effort to remove unbelief and all other hindrances to the enjoyment of God's rest. To help them in this, God has given them the Scriptures. His living Word penetrates into the heart, separates the merely natural from the truly spiritual, and exposes people as they really are before God (11-13).
Verse 15
A high priest for the faithful (4:14-5:10)
Because people were in danger of denying their Christian faith and going back to Judaism, they are reminded that Christ's priesthood is incomparably superior to Aaron's. Christ needs no tabernacle or temple, for he has passed through the heavens and into the presence of God. Through him, believers also may enter this presence, and ask God's help during their temptations. They can depend upon Christ, because being man he can sympathize with them, and being God he can give them super-human aid (14-16).
The Israelite high priest, since he acted on behalf of the people, needed to have a sympathetic nature and an awareness at all times that he too was a sinner who needed God's forgiveness. His high priesthood was an office to which he was appointed, not one he chose for himself (5:1-4). All this was true of Christ, except that he, having no sin, did not offer sacrifices for his own cleansing (see 7:26-28). He was God's Son, appointed by God to an eternal priesthood (5-6; for the priesthood of Melchizedek see 7:1-28).
Jesus Christ participated in the normal experiences of earthly life. In so doing he learnt the full meaning of obedience to his Father's will, even though it led to suffering and death (7-8; cf. Matthew 26:36-46). Having fulfilled in practice God's ideal of human perfection, he is completely qualified to carry out his God-given work of saving and helping those who submit to him (9-10).