Revelation 20:11–15 occurs just after the end of the kingdom reign of Christ on earth, when Satan was released for a brief time. He gathered rebel forces together to battle God and His saints, but lost and was cast into the lake of fire (Revelation 20:7–10). The next event described by John is the judgment at the great white throne. This is the point where unbelievers are judged according to their actions—a death sentence for everyone not saved through Christ (Romans 6:23). Chapter 21 describes the descent of the New Jerusalem from heaven and the beginning of the eternal age.
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“Revelation 20:15” Bibleref.com
15 If anyone was not found written in the book of life, he was cast into the lake of fire.