So an angel comes down from heaven with a key, and the angel chains Satan in the abyss for a thousand years.
And there is one thousand years of peace, when the saints reign with Christ.
Ever heard of "the millennium"? Right here in Revelation, Chapter 20, is the millennium, the thousand-year reign of Christ.
There are several schools of thought about the millennium. Some people believe that there will be a literal 1,000 year reign of Christ. The pre-millennial view is that Christ will come before the thousand year reign, and that he will take believers away (rapture) before the tribulations. The "post-millennial view" is that Christ will come at the end of the 1,000 years, a time of peace (maybe not a literal thousand years) during which most people will become Christian.
Others (including most Lutherans, by the way) believe that the millennium is not literal, but that the 1,000 years represent the entire church age. "Amillenialism teaches that good and evil, the kingdom of God and the kingdom of Satan, develop simultaneously and grow until the end of this age." (this sentence is from an old book on The Revelation by Esther Onstad, "Courage for Today/Hope for Tomorrow."
At the end of the 1,000 years, Satan is loosed again briefly, and then, the new heaven and the new earth arrive. God will dwell with God's people in a new creation that is what God intended in the first place. There is no longer any death or darkness, the holy city is replendent with jewels and wealth, and God will wipe away every tear from the eyes of those who have suffered and have been persecuted and have been vilified in this life.
So the basic message of the book of Revelation is this: even when the world looks darkest and most frightening, even when God's people are being persecuted and killed, the victory belongs to God and the Lamb.
At the very end of the book of Revelation, the Prayer is this:
Come, Lord Jesus.