The thousand-year kingdom is not the end. Revelation 20:7–15 describes a last test, the destruction of Satan and the final judgement; the eternal age that follows is described in scattered verses, not in one place.
Satan Loosed for a Little Season
And when the thousand years are expired, Satan shall be loosed out of his prison…
— Revelation 20:7
He goes out to deceive the nations called Gog and Magog. These are not the Gog of the war at the start of the seven years: they are the people Satan deceives in this 'little season'.
In the thousand years each generation is better than the last, but a few at the end still carry bad qualities that never showed, because everything around them was good. Satan draws them out, and they turn against God. How long the little season lasts we are not told: perhaps a few years, perhaps fifty or a hundred, which is still short beside a thousand.
Fire comes down from God out of heaven and devours them (Revelation 20:9). Only those Satan could not deceive remain on the earth. Adam was made perfect in body, but God's Spirit was not yet in him. These people have a good nature and the Holy Spirit as well, because the gospel reached them and they believed and were baptised. We stand between: our nature is sinful, so Satan can deceive us, and he accuses us before God and is allowed to test us. Once this last test is over he has nothing left to do, and he is thrown into the lake of fire.
The Lake of Fire and the Second Death
Matthew 10:28 speaks of two deaths. Killing the body is the first. Destroying the soul is the second. When the body dies the soul leaves it and waits, in the realm of the dead or in the place of comfort above, until the resurrection. It is not destroyed until it is thrown into the lake of fire, and that is the second death.
So Satan, though a spirit, will die there: 'thou shalt be a terror, and never shalt thou be any more' (Ezekiel 28:19). Anyone thrown in is destroyed so completely that even the memory of him goes (Job 24:20). If he lived on in the fire for ever, he would in effect have eternal life, though in pain, and Scripture does not teach that.
Revelation 20:10 says the torment is 'for ever and ever' (sada sarvakal). That is not eternity (anant kaal): sada sarvakal has a limit, and anant kaal has none. The torment lasts the whole length of the punishment, without relief, and then the soul is destroyed. The lake of fire is not eternal either; it serves until Satan and the wicked are destroyed.
The Great White Throne
After the little season, those still held by 'death and hell', the realm of the dead, are raised and stand before the throne (Revelation 20:11–15). This is a resurrection for judgement, not for life. Books are opened, and so is the book of life, which is the Lord Jesus Christ. Everyone in him enters eternal life; to the rest he says that they are not his.
And whosoever was not found written in the book of life was cast into the lake of fire.
— Revelation 20:15
Judgement here is to punish, not to reward. Each is judged by his works, and the more evil he did, the greater his punishment. All are cast into the lake of fire, but the punishments differ, and when each ends, that soul is destroyed. Thrown in beside Satan, they say to him, 'Art thou also become weak as we?' (Isaiah 14:10), and they grieve at their own choice: 'How have I hated instruction, and my heart despised reproof' (Proverbs 5:12).
The Eternal Age
The earth remains. 'While the earth remaineth, seedtime and harvest… shall not cease' (Genesis 8:22). Only people sow and reap, so the people Satan could not deceive live on the earth as Adam did before he sinned, eating and drinking, while those with glorious bodies need not.
Death is gone: 'The last enemy that shall be destroyed is death' (1 Corinthians 15:26). Death still exists in the thousand years, but not in the eternal age. When their lives end, people on the earth are transformed and taken up, as Enoch was, to join God's church in glorious bodies, and the next generation follows. Psalm 72:7 promises abundant peace until the moon is no more; what comes between the moon's going and the earth's we are not told.
Then the earth wears out 'like a garment' (Psalm 102:25–26; Isaiah 51:6): as cloth gets holes and tears, the earth will break apart. Heaven and earth shall pass away, but not the Lord's words (Mark 13:31). After that, those still living are taken up to the Lord, and God's people never perish: their life is eternity.
What they do then is not stated clearly. Deuteronomy 4:19 says the Lord has 'divided' the sun, moon and stars among the people under heaven, so perhaps the reign will be over the stars, but we see only dimly. An heir is no different from a servant while he is a child (Galatians 4:1–7); when he grows up he takes his authority. We now have less power. Then we shall have full power and be like God. More will be made known at the marriage feast, where the Word is the food.
The Closing Words of Revelation
Revelation 22 closes the book. The Lord says 'I come quickly; and my reward is with me, to give every man according as his work shall be' (Revelation 22:12). The wicked will not change, while the good grow better. Those who have washed their robes, that is, taken salvation, enter the city by the gates to eat of the tree of life, and the wicked stay outside and are destroyed. Nothing is to be added to this book or taken from it.
And the Spirit and the bride say, Come… And whosoever will, let him take the water of life freely.
— Revelation 22:17
The Spirit and the bride, the church, call people to salvation and the forgiveness of sins.
Takeaway
The Lord has shown us beforehand what lies ahead, and all of it will come. The work for today is plain: the church is to tell the gospel, and each of us is to live his life well.