Many scriptures depict God's elect reigning over various peoples throughout the millennium. The question is often raised as to who are these millennium people, and where did they come from? One possibility is that the people of the millennium are the souls of the dead.
Clearly, there will be people, both righteous and unrighteous, in the world during the millennium period. One question that is often raised with respect to these millennium people, is who they are, and where did they come from? In addressing this question there are many possible explanations, but there are two explanations that appear to be the most probable in light of the scriptural evidence.
The first possibility, is that the people of the millennium are not flesh and blood people, but the spirits or souls of those who have lived in prior generations. Thus, the millennium will be a spiritual time when people no longer live in the flesh. The other possibility is that after the tribulation and the return of Christ, some people will be left in the world to repopulate it. So the nations of the millennium are the descendents of those who survived both the tribulation period, and the return of Christ.
In the New Testament, we are presented with some important information that will help us to better understand the nature of the millennium. This information relates to the resurrection of the dead, and its timing with respect to the millennium. 1st Corinthians 15 tells us that the first resurrection of the dead will happen at the last trumpet, "Behold, I shew you a mystery; We shall not all sleep, but we shall all be changed, In a moment, in the twinkling of an eye, at the last trump: for the trumpet shall sound, and the dead shall be raised incorruptible, and we shall be changed" (1st Corinthians 15.51-52 KJV bible).
We understand from this passage that Christians will be raised incorruptible at the last or seventh trumpet, which is the moment when Christ returns (Revelation 11.15). Therefore, if we know that the millennium also starts at Christ's return (Revelation 19-20), then the faithful will have already been resurrected into spiritual bodies during the millennium. However, that only addresses the state of God's elect during the millennium. We still haven't identified who are the people or nations they will be reigning over throughout the millennium.
We know from Revelation 20.4-6, that only the faithful overcomers will reign with Christ during the millennium. It also indicates that none of the dead will be changed or resurrected until after the millennium is over. Thus, the dead will exist as disembodied souls throughout the millennium period, "...and I saw the souls of them that were beheaded for the witness of Jesus...and they lived [or came to life] and reigned with Christ a thousand years. But the rest of the dead lived not again until the thousand years were finished. This is the first resurrection. Blessed and holy is he that hath part in the first resurrection...they shall be priests of God and of Christ, and shall reign with him a thousand years" (Revelation 20.4-6 KJV bible). Could these dead ones being indentified here be the nations or people of the millennium?
Many passages lead to that conclusion. They indicate that during the millennium there will not be new people in the world, but rather people who have lived before. These scriptures indicate that when Christ returns and the millennium begins, it will be the souls from prior generations who are the millennium nations. These bodiless souls will live in the world and interact with God's elect, even though they are in a state of spiritual captivity to Hades and death (Revelation 20.13). So what will take place in the millennium is kind of mingling between God's elect and the souls of the dead. The spiritual dead from the outer darkness will submit themselves to the faithful in God's Kingdom, so that they may learn the ways of the Lord.
One passage that points to this "spiritual millennium" is Luke 12, which depicts Christ rendering justice after his return, "And that servant, which knew his lord's will, and prepared not himself, neither did according to his will, shall be beaten with many stripes. But he that knew not, and did commit things worthy of stripes, shall be beaten with few stripes" (Luke 12.47-48 KJV bible). This passage describes how Christ will judge the ones who know his will to a higher standard than those who don't. Rather than the white throne judgment, it must refer to the millennium, because it describes different degrees of punishment, or stripes, for different individuals.
If we accept the millennium context of this scripture, then the question becomes who are these people that he is rendering justice upon. They are clearly not his faithful servants from the first resurrection, because the faithful will be rewarded and reign with him. What it describes are both unbelievers and apostates receiving stripes for their previous earthly lives. Thus, we are left to conclude that the souls of dead will be present in the world during the time of the millennium.
This same reasoning holds true for another millennium scripture, "Then shall ye begin to say, We have eaten and drunk in thy presence, and thou hast taught in our streets. But he shall say, I tell you, I know you not whence ye are; depart from me, all ye workers of iniquity. There shall be weeping and gnashing of teeth, when ye shall see Abraham, and Isaac, and Jacob, and all the prophets, in the kingdom of God, and you yourselves thrust out" (Luke 13.26-28 KJV bible).
As with similar passages, we have here a depiction of the world after the second advent, in which Christ receives his elect servants to him, and casts the false and disloyal servants into the darkness. In verse 27, he rebukes the unfaithful based on the evil deeds that they have committed in life. If we know that only God's elect will partake in the first resurrection (Revelation 20.4-6), then how do we account for these castaways being in the world and pleading with Christ? How could some of those who literally knew Jesus be rebuked by him after his return? Thus, the scriptures entail a spiritual millennium, in which the vestigial souls of people who have lived before will populate the world.
Jesus' return will certainly be a cataclysmic event that affects all life on earth, "And this shall be the plague wherewith the LORD will smite all the people that have fought against Jerusalem; Their flesh shall consume away while they stand upon their feet, and their eyes shall consume away in their holes..." (Zechariah 14.12 KJV bible), "And every island fled away, and the mountains were not found. And there fell upon men a great hail out of heaven..." (Revelation 16.20-21 KJV bible).
However, even though the natural world will be devastated when Jesus returns, the spiritual world will still remain. This is why in Matthew 8, the demons cry out saying, "...What have we to do with thee, Jesus, thou Son of God? art thou come hither to torment us before the time?" (Matthew 8.29 KJV bible). The demons speak of a future time in which they will be tormented. This "time" that they are dreading is the second advent, when Christ will reign over all his enemies. So we understand that when Christ returns, men will die in the flesh, but their collective spiritual reality will continue on. At this time, wicked spirits and souls will be tormented by the glory of Christ, "The same shall drink of the wine of the wrath of God...and he shall be tormented with fire and brimstone in the presence of the holy angels, and in the presence of the Lamb" (Revelation 14.10 KJV bible).
The idea that the souls of the dead will play a role in the millennium is also supported in other places. Notice what Christ says in Revelation 3, "Behold, I will make them of the synagogue of Satan, which say they are Jews, and are not, but do lie; behold, I will make them to come and worship before thy feet, and to know that I have loved thee" (Revelation 3.9 KJV bible). This passage clearly describes a future time when those who have mistreated Christ's servants are forced down in submission to them. This is also similar to Isaiah 60, "The sons also of them that afflicted thee shall come bending unto thee; and all they that despised thee shall bow themselves down at the soles of thy feet" (Isaiah 60.14 KJV bible). We know that such a forced subordination can only take place after Christ has made the world drink the wine of his wrath.
However, these prophecies cannot be interpreted as being post-judgment, because after Judgment Day the unredeemed will not have any place in the world (Revelation 21.8). Thus, we are left to conclude that the souls of people who have acted wickedly will be in the world during the millennium. They will spend the millennium in a state of forced submission, feeling misery or even torment, as they are made to eat the fruits of their unrighteousness.
There is still more evidence for the souls of the dead being the millennium nations. Notice the response that Jesus gives to the high priest, when he is being accused, "...Art thou the Christ, the Son of the Blessed? And Jesus said, I am: and ye shall see the Son of man sitting on the right hand of power, and coming in the clouds of heaven" (Mark 14.61-62 KJV bible). Jesus' statement is interesting, because it implies one of two things. Either that his glorious return was so imminent, that it would happen before the high priest died. However, this is a stretch, even for the preterist interpretation. That leaves the other possibility, which is that the entire world, including people from past generations, will somehow witness his return. This implies that in the cataclysm of Christ's return, the spiritual reality that is currently unseen, will become the de facto reality of the millennium.