REVELATION 21:24, 26
It is important to for us to remember that Revelation 21-22 is discussing things “after” the creation of the new heavens and earth. These chapters are interspersed with things of both the seen (church) and unseen (heavenly) realms, and we need to correctly interpret which things are being spoken of which realm.
There is an earthly aspect to the New Jerusalem, as well as a heavenly one. It is not an either/or scenario (i.e., “only in heaven” or “only on earth”). It is a both/and situation. The nations on earth certainly walk by the light of that heavenly city and bring their glory into it, but it is still a heavenly city that receives that glory. How do the nations bring glory to God who dwells in the unseen realm? It is twofold:
1) Saved souls themselves are treasure (Isa. 60:3, 7, 10-11, 66:19-20). Note how Isa. 66:19-20 describes Gentiles being saved from all the nations are like an “offering” to the Lord. This could be easily understood as an analogy to the Hebrew, who are very familiar with offerings to the Lord, and could easily be understood by Israel as the antitype/symbolism of their grain offering in their physical temple.
It is indeed glorious to see the nations becoming Christians, spreading the gospel of the Kingdom, and converting all cultures to Christianity. However, the real glory will be seen once we get to heaven to see the full impact of the spiritual riches that were stored up in heaven by those nations.
2) Each believer stores up personal spiritual riches in heaven (Matt. 6:20; Luke 12:33; Mark 10:21).
[For a more in-depth study see eschatology “Study Series 16 Lesson 9 Rev. Chapter 21”]