Revelation 20:3

For such are false apostles, deceitful workers, transforming themselves into apostles of Christ. And no wonder! For Satan himself transforms himself into an angel of light. Therefore it is no great thing if his ministers also transform themselves into ministers of righteousness, whose end will be according to their works. (2Cor. 2Cor. 11:13-15)

This is his pattern: misrepresentation of truth through deception so those who respond to his promises always wind up with unforeseen liabilities which attend participation in his schemes. His two greatest tools are temptation and compromise. See commentary on Revelation 13:14.

till the thousand years were finished
What an amazing time of blessing this will be! Satan and his demonic realm will be rendered completely inoperative during the coming earthly kingdom of God. But this great blessing also has a flip side: in the removal of the great tempter is the removal of a convenient excuse by which men hide their own rebellious nature. And this, it would seem, is part of God’s plan in locking Satan away for the duration of the Millennial Kingdom—to show man his utter incapability of obedience to God, even in the midst of ideal conditions and in the absence of the influence of the serpent of old.

But after these things he must be released for a little while.
After the thousand years have expired, he is released to deceive the nations one final time. Here we see the sovereignty of God Who uses all things to achieve His ultimate ends. Satan is no less a tool of God in his rebellion than in his obedience. Although God is not the author of sin, His sovereignty over the affairs of history is not the least threatened by the disobedience of His creatures. See commentary on Revelation 20:7.

Notes

¹ Frederick William Danker and Walter Bauer, A Greek-English Lexicon of the New Testament and Other Early Christian Literature (Chicago, IL: University of Chicago Press, 2000), 283.

² Alva J. McClain, The Greatness Of The Kingdom (Winona Lake, IN: BMH Books, 1959), 481.