Q. Would you please explain why Satan is released from the bottomless pit for a short time at the end of the millennium? Why doesn’t Jesus just throw him into the lake of fire right away?
A. The Bible doesn’t tell us, so this is only my opinion. I think one purpose of the Millennium is to demonstrate that even with Satan bound, all unbelievers gone, and Jesus ruling in their midst, eventually natural man’s sin nature will cause him to rebel against God. Freeing Satan at the end of the Millennium proves this, because he’ll be able to recruit a large army to attack God’s people (Rev. 20:7-9).