We may not know every reason why God chooses to allow Satan to be released and have one more battle, but the main reason is clear—God will use this final release of Satan to mark an end of evil and sin. With sin and Satan removed, the curse of sin will end and God’s people will dwell with Him for eternity in a perfect, sinless new heaven and earth.
Revelation 20:7–8 notes, “And when the thousand years are ended, Satan will be released from his prison and will come out to deceive the nations that are at the four corners of the earth, Gog and Magog, to gather them for battle; their number is like the sand of the sea.” Following the millennial kingdom (the 1,000 year reign of Christ), God will allow Satan to be released and gather unbelievers to battle against the Lord and His people, but why?
Though not every detail is given, the Bible does give some indication of God’s purpose behind this plan. In Revelation 21—22, God creates a new heaven and new earth where there is no curse or sin. Prior to doing this, He chooses to remove the devil, beast, false prophet, and those who follow them. Revelation 20:9–10 states, “Fire came down from heaven and consumed them, and the devil who had deceived them was thrown into the lake of fire and sulfur where the beast and the false prophet were, and they will be tormented day and night forever and ever.”
Who are the unbelievers living during this period? At the end of the tribulation period, some people who believed in Jesus during the tribulation will still be alive and will enter the millennial kingdom alive rather than coming from heaven to earth with the Lord. These individuals will marry and have children. Apparently, some of these children will choose not to believe in the Lord and will eventually side with Satan in the final battle following Satan’s release in Revelation 20. There will apparently be many unbelievers still on the earth at this time, since verse 8 describes them as “the nations that are at the four corners of the earth, Gog and Magog, to gather them for battle; their number is like the sand of the sea.”
Once Satan and all of those not in the book of life are removed, God will then be prepared to create a new heaven, new earth, and new holy city (21:1–2). Since sin and Satan have been removed, God can now come and live among His people (v. 3). No curse of sin will continue (v. 4). All things will be new (v. 5).