All of those dead saints, who took part in the FIRST RESURRECTION (Rev.20:6), were from among the saints who died before the Parousia in AD 66-70. Among these were the special groups of Old Testament and Transition period MARTYRS. They are:
(a) The souls of those who had been beheaded (martyred) for Christ and the Word. This most likely would also have included the Old Testament martyrs who “lived” or were made alive again (not their resurrection) out of the graves to witness to the first century Jewish people at the time of Christ’s RESURRECTION (Matt. 27:52-53):
“The tombs were opened, and many bodies of the saints who had fallen asleep were raised; and coming out of the tombs after His resurrection they entered the holy city and appeared to many.”
John the Baptist, who was literally beheaded for his testimony, would likely also be included in this O.T. group. They ascended with Christ to “under the altar” in the unseen heavenly realm at His ascension forty days later (Eph. 4:8).
(b) The souls of those who did not bow before the beast or his image and did not receive the mark of the beast. These may be those transition martyrs who were killed and were sent on an individual basis to the unseen realm where they also were temporarily placed “under the altar.” These would have included saints like Stephen, James, Peter, Paul, and John. Upon their deaths, they joined the other martyrs already there (Rev.6:9-11; 7:13-17; 20:4).
I believe the Bible further supports that the First Resurrection occurred at the resurrection of Jesus in 1 Corinthians 15. Notice what apostle Paul says about this and the millennial reign in his great discourse on the resurrection of the dead ones in 1 Cor. 15:23-26. I believe this passage alone dispels any doubts about the 40-year millennium concept (see “Millennium”) for a deeper look into this). Notice what he says in verse 25 in particular:
1Cor. 15:23 “But each in his own order: Christ the FIRST FRUITS, after that those who are Christ’s at His coming,
1Cor. 15:24 then comes the end, when He hands over the kingdom to the God and Father, when He has abolished all rule and all authority and power.
1Cor. 15:25 For HE MUST REIGN UNTIL He has put all His enemies under His feet.A
1Cor. 15:26 The last enemy that will be abolished is DEATH.”
A the Greek text in 1 Corinthians 15:25 “for he must reign” is a present infinitive verb, denoting that action is occurring during the time of Paul’s writing….one could say, “for it behooves him to keep reigning until….” This assumes that the “reign” of Christ was a reality at the time of Paul’s writing.
When we compare Rev 20:6-14 with 1Cor 15:23-26, we see the exact same ideas in both texts:
(1) Christ and His first fruits were raised first (first resurrection).
(2) He reigns with those saints until the End (of the millennium).
(3) All of His enemies, including DEATH, were crushed by the End of His reign.
As we saw, that first resurrection was mentioned briefly (without detail) in Matthew 27:52-53. I believe those were martyrs that were raised at the same time as Christ. They appeared in Jerusalem for forty days, just like Christ did, and then ascended with Him (like Eph. 4:8-9 implies). When He ascended with those martyrs, He deposited them under the altar in the heavenly temple (Rev. 6:9), and then ascended the rest of the way to the Highest Heaven (the Holy of Holies) to present His blood on the heavenly mercy seat.
All of these disembodied martyr’s souls possibly had some kind of temporary spiritual bodily form like Samuel when he appeared to the necromancer (medium) at En-Dor (1 Sam.28:7), or like Moses and Elijah when they appeared to Jesus at the Transfiguration (Matt. 17:1-3).
“9When He opened the fifth seal, I saw “under the altar” THE SOULS of those who had been slain for the word of God and for the testimony which they held, 10And they cried with a loud voice, saying, “How long, O Lord, holy and true, until You judge and avenge our blood on those who dwell on the earth?” 11Then a WHITE ROBE was given to each of them; and it was said to them that they should rest a LITTLE WHILE LONGER, until both the number of their fellow servants and their brethren, who WOULD BE KILLED as they were, WAS COMPLETED.” (Rev.6:9-11).
These martyred souls reigned with Christ during the transition period. They still had to be RESURRECTED from their temporary spiritual bodily state to their eternal individual immortal heavenly bodily state. They waited in the unseen realm reigning with Christ. They had already passed out of judgment (and the second death) because of their faithfulness under the persecutions (John 5:24). They had already been judged faithful by their martyrdom (Rev.20:4).
They would not have received their new permanent incorruptible, immortal, heavenly bodies until the Parousia when the Rest of the Dead saints who had died of natural causes (all who were not martyrs) were raised and given their new immortal bodies. These martyrs certainly were blessed and they received special treatment from the Messiah (Rev.20:5-6).
Then at the Parousia, when Christ descended from heaven in AD 66, He brought those martyrs with Him (as 1 Thess. 4:15 teaches) and then raised the rest of the righteous dead out of Hades/Sheol into their new immortal bodies in the unseen realm, changed the living into the unseen realm and into their new immortal bodies (1 Cor. 15:51-54), and then caught them all up together into the glory cloud above to remain with Him forever afterwards (1 Thess. 4:17). AD 70 was certainly the END that Paul was referring to in 1 Cor. 15:23-24. Those who were Christ’s is referring to those Christians who had died during the forty year transition period (AD 30-70). They were raised at the Parousia. This included both Jewish and Gentile Christians who died during that time.
[Also see: “Millennium” also “Resurrection (General)”]
[For a more in-depth study see eschatology “Study Series 16 Lesson 8 Rev. Chapter 20 (sub study on Millennium)”]