What does Hebrews 12:29 mean?

The prior verse referred to God's kingdom as one that "cannot be shaken." This was a contrast to the world we live in today, which shook when God brought the old covenant (Exodus 19:9–20) and which will one day be destroyed and replaced (Revelation 21:1). The phrasing of that verse showed how we receive that kingdom by grace, and the same grace is what allows us to approach and honor God (Hebrews 4:16).

Here, the writer of Hebrews employs an image used earlier in this letter. Hebrews 10:26–27 referred to God using "a fury of fire," indicating His wrath on those who defy Him. Hebrews 6:7–8 similarly pointed out that a field which cannot produce good crops is suitable only to be burnt—a painful but purifying way of restoring it to its intended purpose. One way or the other, God's holiness will eliminate everything temporary and worthless, leaving only what is eternal and according to His will (Matthew 6:20; 1 Corinthians 3:15; Numbers 31:23). That judgment also separates those who reject God from His eternal kingdom (2 Thessalonians 1:8–9).

As always, the writer of Hebrews relies on God's established Word to make his arguments. This reference to God being "a consuming fire" is a quotation from Deuteronomy 4:24.

The following verses, part of the last chapter in the book of Hebrews, will build on this idea by reminding the readers about practical steps for living out a faithful trust in God and our place under the new covenant.