What is the bottomless pit where Satan is confined?
The bottomless pit is a unique place known only to God where Satan is confined for the thousand-year period. It is not the Lake of Fire, which is eternal, because Satan must later be released for a little season. He is shut up and sealed there so he cannot deceive the nations until the thousand years are fulfilled.
Les explains that the bottomless pit is a unique place known only to God, not the Lake of Fire, because the Lake of Fire is a place of eternity. Satan is not ready for eternity yet; he has one more opportunity at the end of the thousand years. So God confines him in the bottomless pit for that thousand-year period, shuts him up, and sets a seal upon him so he should deceive the nations no more until the thousand years are fulfilled. After that, he must be loosed for a little season. The millennium then becomes another period of testing, the seventh, since God always does things in seven, when Satan will test the new generations in that kingdom economy.