Invaders, page-23

What's your thoughts as to why God releases satan for a short time, why release at all?
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By the end of the Thousand Year Reign, all earth will have come to resemble the original Eden. Perfect mankind will no longer need a high priest to intercede for it before God, since all traces of Adamic sin will have been removed and the last enemy, death, brought to nothing. It is now time for a final test. Will that perfected world of mankind, in contrast with the first humans in Eden, stand firm in its integrity?
Sadly, not all will.
Do not forget that Satan was able to mislead the perfect Adam and Eve while they were enjoying life in the Paradise of Eden. And he was able to lead astray heavenly angels who had seen the bad results of the original rebellion. The number of those who join Satan in his revolt will be “as the sand of the sea.”
(Revelation 20:7, 8) Now as soon as the 1,000 years have ended, Satan will be released from his prison, 8 and he will go out to mislead those nations in the four corners of the earth, Gog and Maʹgog, to gather them together for the war. The number of these is as the sand of the sea.

Rather than being merely abyssed, this time Satan, the original serpent, will actually be crushed out of existence, pulverized, completely annihilated as if by fire as will all who side with him in his rebellion.