In the book of revelations it says after the devil is captured in the war of heaven and earth he is imprisoned by an angel for a thousand years then let go for a little while why let him go?

By the end of the Thousand Year Reign, all earth will have come to resemble the original Eden. It will be a veritable paradise. 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. Christ's Kingdom will have achieved God's purpose to create one world with one government. At this point, Jesus "hands over the kingdom to his God and Father."-1 Corinthians 15:22-26; Romans 15:12. 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? John tells us what happens: "Nowas soon asthe thousand yearshave been ended,Satan will belet loose outof his prison,and he willgo out tomislead those nationsin the fourcorners of theearth, Gog andMagog, to gatherthem together forthe war. Thenumber of theseis as thesand of thesea. And theyadvanced over thebreadth of theearth and encircledthe camp ofthe holy onesand the belovedcity. But fire came down out of heaven and devoured them."-Revelation 20:7-9. Each person there at that time will be perfect, in the same state as were Adam & Eve when they failed their test. Each person will have the opportunity to once and for all time to show where they stand on the issue of the universal sovreignty of Jehovah God.