The peoples of God in Revelation 21 are a remnant of the sheep described in Matthew 25:31-46. When the Lord Jesus comes back, He will sit on His throne of glory in Jerusalem and will gather all the living, different peoples of the nations to Him. They will be classified into sheep and goats, and He will judge them. The goats, who are on His left hand, will go directly to the lake of fire. The sheep, on His right, will inherit the thousand-year kingdom, which God prepared for them from the foundation of the world. We were predestinated unto sonship before the foundation of the world, but the millennium was prepared by God for these sheep from the foundation. There is a difference.
This judgment will not be at the great white throne (Rev. 20:11), which follows the millennium. It will be at the throne of Christ's glory before the thousand years. The judgment will not be according to the law of Moses nor according to the gospel of grace, but according to the eternal gospel (Rev. 14:6-7). Many Christians have never heard of the eternal gospel. It does not include redemption nor the forgiveness of sins. It comprises two things: to fear God and to worship Him. This gospel will be preached by an angel at the time of the great tribulation, which will last three and a half years. This is the time when Antichrist will do all he can to persecute the Jews and the Christians. In Matthew 25, according to the verdict of Christ's judgment, the Jews and the Christians will be treated quite well by the sheep (vv. 34-36). But a great many will follow Antichrist in persecuting the Jews and the Christians. Christ will make His judgment accordingly, and that judgment will be according to the eternal gospel.
The sheep will be transferred into the millennial kingdom to be the peoples, and the overcoming saints will be kings over them (Rev. 20:4, 6). The sheep will be restored to the original state of man as created by God and will be citizens of the millennial kingdom, enjoying the blessing of the restoration (Acts 3:21). Restoration is not regeneration. To be regenerated is to be born again with another life, God's life, but to be restored is to be brought back to the original state of God's creation.
At the end of the thousand years Satan, after being released, will instigate the last rebellion against God (Rev. 20:7-9). Many of the sheep will join Satan's rebellion and will be burned with fire from heaven. The remnant of the sheep will be transferred to the new earth to be the nations (Rev. 21:24). God will tabernacle with them, the peoples (Rev. 21:3). They will be ruled by the sons of God as kings (22:5). To them there will be no more death, sorrow, crying, pain, or curse (21:4; 22:3a). They will be sustained eternally by the leaves of the tree of life (22:2). We will eat the fruit, but the nations will enjoy the leaves. They will walk by the light of the holy city (21:24a). With their kings they will bring their glory and honor to the city. They will respect the city and regard it as superior.
The saints throughout all the dispensations who have been redeemed will be the reborn ones, God's sons, belonging to the royal family. They will be kings in eternity. The restored remnant of the unbelievers will be the peoples, the nations, walking in the light of the city and ruled by the saints. Another category of people is the perished ones. The perished unbelievers will be in the lake of fire (21:8). This gives us a general view of the new heaven and new earth.