"In these verses we have a description of the binding of Satan. The dragon, here clearly identified as “the devil, Or Satan,” is said to be bound for a thousand years and then cast into a place called “the Abyss.” The purpose of this binding is “to keep him from deceiving the nations any more until the thousand years were ended.”
"The book of Revelation is full of symbolic numbers. Obviously the number “thousand” which is used here must not be interpreted in a literal sense. Since the number ten signifies completeness, and since a thousand is ten to the third power, we may think of the expression “a thousand years” as standing for a complete period, a very long period of indeterminate length.
"In agreement with what was said above about the structure of the book
(in the article) and in the light of verses 7-15 of this very chapter (which describe Satan’s “little season,” the final battle and the final judgment), we may conclude that this thousand-year period extends from Christ’s first coming to just before his Second Coming.
"Since the “lake of fire” mentioned in verses 10, 14 and 15 is obviously a description of the place of final punishment, the “Abyss” mentioned in verses 1 and 3 must not be the place of final punishment. The word Abyss should rather be thought of as a figurative description of the way in which Satan’s activities will be curbed during the thousand-year period.
"What is meant, then, by the binding of Satan? In Old Testament times, at least in the post-Abrahamic era, all the nations of the world except Israel were, so to speak, under Satan’s rule. At that time the people of Israel were the recipients of God’s special revelation, so that they knew God’s truth about themselves, about their sinfulness, and about the way they could obtain forgiveness and salvation.
"During this same time, however, the other nations of the world did not know that truth, and were therefore in ignorance and error (see Acts 17:30) — except for an occasional person, family or city which came into contact with God’s special revelation. One could say that during this time these nations were deceived by Satan, as our first parents had been deceived by Satan when they fell into sin in the Garden of Eden.
"Just before his ascension, however, Christ gave his disciples his Great Commission: “Go and make disciples of all nations” (Mt. 28:19, NIV). At this point one can well imagine the disciples raising a disturbing question: How can we possibly do this if Satan continues to deceive the nations the way he has in the past?
"In Revelation 20:1-3 John gives a reassuring answer to this question. Paraphrased, his answer goes something like this: “During the gospel era which has now been ushered in, Satan will not be able to continue deceiving the nations the way he did in the past, for he has been bound. During this entire period, therefore, you, Christ’s disciples, will be able to preach the gospel and make disciples of all nations.”
"This does not imply that Satan can do no harm whatever while he is bound. It means only what John says here: While Satan is bound he cannot deceive the nations in such a way as to keep them from learning about the truth of God.
"Later in the chapter we are told that when the thousand years are over, Satan will be released from his prison and will go out to deceive the nations of the world to gather them together to fight against and, if possible, to destroy the people of God (verses 7-9).
"This, however, he cannot do while he is bound. We conclude, then, that the binding of Satan during the gospel age means that, first, he cannot prevent the spread of the gospel, and second, he cannot gather all the enemies of Christ together to attack the church."
More at:
Amillennialism: Part I – Introduction by Anthony Hoekema