The millennial kingdom is the name given to a time of thousand years after the return of Christ. It is possible that these thousand years represent a symbolic period that can even be greater or lesser than thousand years. After the tribulation, Jesus will return (Matthew 24:29), and there will be the first resurrection of all the people who will inherit eternal life (Revelation 20:4-6; 1 Thessalonians 4:16) and the so called “rapture” of the resurrected and of those still alive at his return (1 Thessalonians 4:17).
Isaiah 65:20 seems to describe a millennial kingdom where sin and curses will still exist; but it is a kind of language that describes the world without sin where the saved will live, through expressions that describe a world in which sin still exists to a lesser extent than the present time.
Only those who have inherited eternal life with eternal bodies will enter in the thousand years; and it is not possible that during that period of time sin and curses will still exist. It is logical to think that at Christ’s return, all the people who will enter the thousand years, including the remnant of the nations that have attacked Jerusalem (Zechariah 14:16), are all converted and with eternal bodies; while all the rest will be destroyed (Zechariah 14:17-18; 2 Peter 3:10-13). As it was in the days of Noah (when only eight people were saved and the others destroyed), so it will be at the coming of Christ (Matthew 24:37-39; 1 Peter 3:20). Therefore, no one will die during those thousand years.
Some people don’t understand if the new earth will be available immediately after Christ’s return (Matthew 19:28; 2 Peter 3:10-13; Isaiah 24:19-20), or after the judgment of the unjust after the second resurrection (Revelation 21:1-2). Matthew 19:28 says that in the regeneration, Jesus will be seated on the throne to judge, which is a parallel of Revelation 20:4 at the beginning of the thousand years. It is clear that the regeneration represents the new heavens and the new earth (Revelation 21:1). This confusion also exists because the visions of the book of Revelation are not all placed in chronological order with respect to each other. In fact, the holy city in Revelation 21:2 is the same beloved city of Revelation 20:9, which will be surrounded by the unjust that will be resurrected after the thousand years. The event of the holy city coming down out of heaven from God (Revelation 21:2), is an event that will take place at the beginning of those thousand years. If after the return of Christ the saved will already have spiritual bodies (1 Corinthians 15:42-50), then it is logical that at that time, they have already entered the spiritual kingdom of God, that is, in the new earth described in Revelation 21:1. And if the new earth is already created at Christ’s return, it is to be excluded that people will die in the thousand years, as this verse confirms: “I tell you this, brothers: flesh and blood cannot inherit the kingdom of God, nor does the perishable inherit the imperishable” (1 Corinthians 15:50).
The redemption of men will cease at the second coming of Christ. After his coming there will be no more people who will have to believe, die and be resurrected. Also, as Revelation 20:6 says, the second death has no power over those who share in the first resurrection. Consequently, all those who will resurrect in the second resurrection, will be hurt by the second death. This also confirms that during the thousand years, there can not be mortal people, who will be redeemed and will inherit eternal life.
There is another reasoning to do: when Christ returns, all people who will share in the first resurrection, and those still alive at his return who will inherit eternal life, will be caught up to meet the Lord in the air (1 Thessalonians 4:16-17), while all the others will be destroyed (Matthew 13:40-42). Those who will not be caught up in the air are unjust that will not have another chance to redeem themselves after Jesus has already returned. It makes no sense to say that the remnant of the nations that will attack Jerusalem before Christ’s return (Zechariah 14:6), and all their descendants, during the thousand years will be present along with those who have been caught up to meet the Lord in the air. This erroneous conclusion makes us think to two classes of people during the thousand years: one with eternal bodies and the other with mortal bodies. If one class has mortal bodies, then it would mean that during that time Satan is able to deceive people and make them die; but this is not possibile, because in the thousand years Satan is bound (Revelation 20:1-2). Moreover, the doctrine which says that the nations deceived by Satan after the thousand years (Revelation 20:8) are persons with eternal bodies is not valid, since God has assured us eternal life without the existence of sin; and this implies that all the saints present in the thousand years can not be deceived.
The vision of the judgment of the great white throne in Revelation 20:11-15 symbolically describes the previous vision of the fire that comes from heaven and devours all the unjust resurrected after the thousand years (Revelation 20:7-9). In conclusion, the millennial kingdom is a phase of time between the first resurrection of the just (Revelation 20:4-6) and that of the unjust (Revelation 20:11-15), which is always part of the kingdom of God (Mark 1:15; Revelation 5:10; Daniel 7:18) or kingdom of heaven (Matthew 3:2) on the new earth (Isaiah 51:6; Isaiah 65:17; Isaiah 66:22; Revelation 21:1). What distinguishes the thousand years from the time after them is that at the end of these thousand years there will be the punishment of the devil in the lake of fire (Revelation 20:10), that of the unjust always in the lake of fire (which is the second death), and the eternal destruction of death and of Hades (Revelation 20:11-15; Isaiah 24:21-22). During the thousand years, Satan, his angels, and all the unjust who will be resurrected in the second resurrection, will be bound, and after these thousand years they will be punished, as confirmed by the following two passages that are related to each other:
21 In that day the LORD will punish the powers in the heavens above and the kings on the earth below. 22 They will be herded together like prisoners bound in a dungeon; they will be shut up in prison and be punished after many days (Isaiah 24:21-22).
1 Then I saw an angel coming down from heaven, holding in his hand the key to the bottomless pit and a great chain. 2 And he seized the dragon, that ancient serpent, who is the devil and Satan, and bound him for a thousand years, 3 and threw him into the pit, and shut it and sealed it over him, so that he might not deceive the nations any longer, until the thousand years were ended. After that he must be released for a little while (Revelation 20:1-3).