Since the original audience of Hebrews was tempted to return to the old covenant and its priestly system and law, the author of the epistle devotes much space to proving the superiority of the priesthood of Christ. Christ’s priestly work is superior to what the old covenant Levitical priesthood could offer, we have seen, because it is grounded in Jesus’ indestructible life and takes place in heaven (7:1–8:5). There is more, however, for today’s passage tells us that the superiority of Jesus’ priesthood is also wrapped up in the superiority of the new covenant that He mediates to God’s people (8:6).
The author takes for granted that Jesus has inaugurated the promised new covenant of Jeremiah 31:31–34, as we will see as we continue studying Hebrews 8. Today we consider what it means that the new covenant is better because it is “enacted on better promises” than the old covenant (Heb. 8:6). John Owen says these better promises are the new covenant promises of Jeremiah 31:33–34 that God will write His law on the hearts of His people and remember their sin no more, that is, finally and fully forgive them. These promises were not fulfilled by the old covenant mediated by Moses. After all, the repeated sacrifices of the Mosaic law mean that the old covenant could not provide full and final forgiveness. They, and the old covenant of which they were a part, could only remind people of sin, not remove it (Heb. 10:1–18). Furthermore, the law demonstrates that the old covenant cannot be the means by which God writes His commandments on the hearts of His people. Deuteronomy 31:14–29 foresees that Israel as a nation would be so corrupt as to break the old covenant. The people would need a new heart, a heart that would come only after the nation of Israel broke the old covenant and suffered the curse of exile (30:1–10).
Nevertheless, the reality of the new covenant promises belonged to the old covenant saints. After all, David, an old covenant believer, enjoyed the complete and final forgiveness of sins in his justification (Rom. 4:5–8). No one is saved except through Christ and His new covenant, which is the ultimate expression of the one covenant of grace between God and His people (John 14:6). The old covenant saints belonged also to the one covenant of grace, though they lived prior to the inauguration of the new covenant. They, no less than us, were redeemed by Jesus alone, though their understanding of this was less full than is ours as new covenant believers.