What does Hebrews 12:23 mean?
In this passage, the writer of Hebrews continues to show that the new covenant is superior to the old covenant. In this case, the emphasis is on the drastically different tone, or mood, of how we perceive those arrangements. The old covenant was given through a dramatic, even terrifying display by God at Mount Sinai (Exodus 19:9–20). In a very deliberate sense, God presented Himself as absolutely holy, and therefore unapproachable to sinful mankind. The new covenant, on the other hand, is presented to us in a much more peaceful, welcoming, and hopeful tone. Christ gives us the ability to "draw near to the throne" without fear (Hebrews 4:16).The last verse mentioned Mount Zion, making reference to both the earthly city of Jerusalem and the upcoming New Jerusalem where believers will spend eternity with God. This verse continues listing the attractive elements of what awaits those who accept the new covenant.
The reference to "the assembly of the firstborn who are enrolled in heaven" is somewhat obscure. The term translated "assembly" here is ekklēsia, which is also frequently translated as "church." Given that these are persons residing in heaven, the indication that they are "firstborn" seems to follow the pattern of verses such as 2 Thessalonians 2:13 and James 1:18, where saved Christians are referred to as the "firstfruits" of God—while an earthly family can only have one "firstborn," all Christians share in this honor as the children of God. Likewise, the reference to being "enrolled" suggests the Book of Life mentioned in Revelation 3:5, Luke 10:20, and Daniel 12:1.
So, the "spirits of the righteous made perfect" would appear to be an additional reference to the assembly of saved souls waiting for those who come to accept Christ.
This is purposefully presented as a contrast to the scenario at Mount Sinai. Rather than God being imposing, unapproachable, and even terrifying because of the implications of the law, those who embrace the new covenant can perceive God as their rescue, their rest, and their joy. All of this is possible only through Christ, who the following verse notes as part of the scene we approach as believers.