THE KINGDOM OF PRIESTS
Revelation 5.10
10. You (Jesus Christ) has made them to be a *kingdom and priests to our GOD (GOD Father), and they will reign upon the Earth.'
~ 10. *Kingdom of priests, holy nation: (Exodus 19.6) (Isaiah 61.6, 66.21) (1Chronicles 29.15) (Psalm 39.12, 119.19) (Hebrews 11.13-16) (Revelation 1.6, 5.10, 20.6).
It looks like that a secret of 24 elders may reveal here, but it is only a guess. If we take it as is that is written about 24 elders, that each of them has a golden crown on their heads (Revelation 4.4), which is the symbol of the authority and the kingship that make them kings, then Jesus "has made them to be a kingdom and priests of our GOD (Father), and they will reign upon the Earth." (Revelation 5.10).
They, 24 elders are not separated kings who will rule the Earth by themselves, but will rule under the Highest King, under the Authority of GOD, and for this reason they cast their golden crowns before the Throne of GOD (Revelation 4.10), submitting their authority as kings and themselves to GOD.
Now the question remain who actually are those 24 elders and kings to whom GOD gave authority to rule the Earth? We know that in the future the king David will return and will rule the nation of Israel as he has done in the past (Jeremiah 30.9) (Ezekiel 34.23-24, 37.24-25) (1Chronicles 28.4) (Hosea 3.4-5).
Ok, if David will rule Israel, and the Apostles of Christ will rule with him judging 12 tribes of Israel (Matthew 19.27-28) (Luke 22.28-30) under Authority of GOD, who will rule the Gentiles?
Because it is written, "the Law will go forth from Zion and the Word of the Lord from Jerusalem," upon entire world, this means that someone have to deliver it to the world and it probably will be the Apostles of Christ or some Prophets of GOD who also preached and prophesied in the past will go to Gentiles.
The number of them perhaps will be 12, the 12 Apostles or the 12 Prophets out of total 24 elders the kings mentioned here, and they are probably mentioned here as the elders. GOD made them as a kingdom of priests, not exclusively as a separate kingdom, but as a body of authority to rule and to enforce the Laws of GOD upon the Earth (10).
Isaiah 2.3
3. "And many peoples will come and say, 'Come, let us go up to the mountain of the Lord, to the House of the GOD of Jacob, that He may teach us concerning His Ways, and that we may walk in His Paths.' The Law will go forth from Zion, and the Word of the Lord from Jerusalem."
~ The Law will come from the Zion: (Isaiah 2.3, 49.6, 51.4) (Micah 4.1-4) (Luke 24.47).
Another 12 out of 24 elders perhaps will be some selected by GOD, Jews or Gentiles or both, to whom GOD also will give authority to rule over the nations of Gentiles and enforce His Laws.
Revelation 20.6
6. "Blessed and holy are those who share in the first resurrection. Over these the Second Death has no power, but they will be priests of GOD and of Christ, and they will reign with Him a thousand years."