The Bible speaks of a "first resurrection" in Rev. 20:4, and in the context it speaks of others coming to life later.
Rev. 20:4 And I saw thrones, and those who sat on them were given authority to judge. Yes, I saw the souls of those executed for the witness they gave about Jesus and for speaking about God, and those who had not worshipped the wild beast or its image and had not received the mark on their forehead and on their hand. And they came to life and ruled as kings with the Christ for 1,000 years. 5
(The rest of the dead did not come to life until the 1,000 years were ended.)
This is the first resurrection. 6 Happy and holy is anyone having part in the first resurrection; over these the second death has no authority, but they will be priests of God and of the Christ, and they will rule as kings with him for the 1,000 years.
If the first resurrection corresponds to the anointed brothers of Christ who are going to be kings and priests with him during the 1,000 years (see verse 6 at the end), what is the purpose of there being another resurrection later during the millenium apart from that one?
Understanding this issue is important because we all have relatives or known people who are already dead and who will resurrect at some point. About them we could ask ourselves the question: will they rise in the first, or in the other resurrection?
What do you think?
This is how I understand it:
The first resurrection, of the Church, occurs before the Great Tribulation, and before Christ's 1,000 year reign (Millennial Age). The first resurrection is described by Paul in 1 Thessalonians 4:15-17 (WEB):
(15) For this we tell you by the word of the Lord, that we who are alive, who are left until the coming [return or presence] of the Lord, will in no way precede those who have fallen asleep [died].
(16) For the Lord himself will descend from heaven with a shout, with the voice of the archangel, and with God’s trumpet. The dead in Christ will rise first,
(17) then we who are alive, who are left, will be caught up together with them in the clouds, to meet the Lord in the air. So we will be with the Lord forever.
The Church has to be resurrected before the Millennial Age because they will be reigning with Jesus during that time. I'm uncertain whether Millennial Age starts before or after the Great Tribulation, but I suspect it's after. The second resurrection, of the rest of mankind, occurs at the start of the Millennial Age. During the Millennial Age the resurrected people (and those who lived through the Great Tribulation) will be gradually restored to perfection. Jesus and the resurrected Christians will be blessing the people during the Millennial Age, and God has set aside 1,000 years for restoring them to perfection.
Christians have to enter through the "narrow (
or difficult) gate" (Matthew 7:13-14) to gain perfection and eternal life, but the rest of mankind have an easier highway to travel over to gain perfection and eternal life. Christians have a short lifetime of difficulty and suffering as a trial for eternal life, whereas the rest of mankind will have 1,000 years of Christ's righteous ruling as their trial, with a final test at the end. Isaiah 35:4-10 (WEB):
(4) Tell those who have a fearful heart, “Be strong. Don’t be afraid. Behold, your God will come with vengeance, God’s retribution. He will come and save you.
(5) Then the eyes of the blind will be opened, and the ears of the deaf will be unstopped.
(6) Then the lame man will leap like a deer, and the tongue of the mute will sing; for waters will break out in the wilderness, and streams in the desert.
(7) The burning sand will become a pool, and the thirsty ground springs of water. Grass with reeds and rushes will be in the habitation of jackals, where they lay.
(8) A highway will be there, a road, and it will be called The Holy Way. The unclean shall not pass over it, but it will be for those who walk in the Way. Wicked fools will not go there.
(9) No lion will be there, nor will any ravenous animal go up on it. They will not be found there; but the redeemed will walk there.
(10) Then Yahweh’s ransomed ones will return, and come with singing to Zion; and everlasting joy will be on their heads. They will obtain gladness and joy, and sorrow and sighing will flee away.”
It is only at the end of the Millennial Age that they will have reached perfection and then they are tested and judged whether or not they are suitable for eternal life. Only then, at the end of the Millennial Age will they have eternal life, so that's why Revelation 20:5 says, "The rest of the dead didn’t live until the thousand years were finished".