Satan conquered. The Last Judgment
In this chapter the visions of the overthrow of Christ's enemies are continued. The devil is bound for 1,000 years (Revelation 20:1-3); the martyrs reign with Christ for 1,000 years (Revelation 20:4-6). It is foretold that, at the end of the 1,000 years, Satan will be loosed, and will make a last assault against the saints, after which he is cast into the lake of fire (Revelation 20:7-10). A vision of the Last Judgment follows (Revelation 20:11-15).
The binding of Satan and the reign of the saints with Christ, both for 1,000 years, is known as 'the Millennium.' Many of the later Jews expected that the Messianic kingdom, of which the prophets spoke, would come in the present age, and they distinguished it from the Pinal Judgment and new heaven of righteousness which would follow. By some it was said that the Messianic kingdom would last 1,000 years, though other periods were also named.
It is plain that St. John made use of this Jewish expectation in his prophecy. But it does not follow that he meant it to be understood literally. It is more in harmony with the character of the book to suppose that he meant this Jewish apocalyptic expectation to be understood spiritually. The same conclusion seems probable from the general circumstances. The Christians had just been told that the persecuting city and empire would be overcome. They might ask whether the devil, the author of all evil would not raise up fresh enemies against them.