Revelation 20:3 had told us that the angel (upon God’s instruction, Psalm 103:20–21; Hebrews 1:14) had locked the abyss and sealed its entry/exit points so that it was escape-proof. The word translated as “released” implies that the door to Satan’s prison is opened from the outside. Satan does not escape; instead, God sets him free. Yet if the Lord sets Satan free, he clearly remains under God’s control.
7 And when the thousand years are ended, Satan will be released from his prison