Therefore, since we are receiving a kingdom that cannot be shaken, let us be thankful, and so worship God acceptably with reverence and awe, for our “God is a consuming fire.” (Hebrews 12:28-29)
We all need something unshakeable in our lives, don’t we? We have this requirement because the sober reality is that our families and relationships, jobs, health, and even our churches—can all be shaken. The only thing that can’t be shaken is God’s kingdom (i.e., His rule through Jesus). The Hebrew writer wants his readers to know that because they belong to Christ, they’re part of something that is going to stand and that’s wonderful news.
At the giving of the first covenant, God’s voice shook the earth (v. 26). The writer says another shaking is coming so that the created things can be removed and what cannot be shaken will remain. It’s possible that this refers to the return of Jesus, but I think you could also make the case that this has to do with the destruction of Jerusalem in 70 AD.
In the context, the two covenants are being discussed. Although the old covenant ends with the death of Christ (symbolized by the curtain in the temple splitting from top to bottom), its remnants still remain. There is still a temple in Jerusalem where priests are offering daily sacrifices. When Titus invades the city, the temple is destroyed (as Jesus predicted in Matthew 24), and the priesthood comes to an effective end with no more sacrifices being offered. The created things are removed so that what is eternal and unshakeable remains.
For people who are wavering between Christianity and Judaism, this is powerful stuff. The writer is telling them it boils down to choosing between something that is obsolete, outdated and ready to disappear (8:13), and something that cannot be shaken. The contrast couldn’t be more pronounced.
Those who are part of the unshakeable kingdom are called to be thankful (v. 29). Acting thankful is good; being thankful is better. They are also told to “worship God acceptably with reverence and awe, for our ‘God is a consuming fire,’” (12:28). James Thompson understands this to be contrasting them with the worshipers under the old covenant for whom something was always missing (9:9, 10:2, 13:10). This is reinforced by 13:15 which tells them, “Through Jesus, therefore, let us continually offer to God a sacrifice of praise,” (13:15). Their worship (like their forgiveness) is ultimate because it is centered in Jesus and therefore should be treated that way.
Out of the unshakeable kingdom flow living sacrifices (Romans 12:1ff).