Then I saw an angel coming down from heaven with the key to the bottomless pit and a heavy chain in his hand.
References for Revelation 20:1
He seized the dragon—that old serpent, who is the devil, Satan—and bound him in chains for a thousand years.
The angel threw him into the bottomless pit, which he then shut and locked so Satan could not deceive the nations anymore until the thousand years were finished. Afterward he must be released for a little while.
Then I saw thrones, and the people sitting on them had been given the authority to judge. And I saw the souls of those who had been beheaded for their testimony about Jesus and for proclaiming the word of God. They had not worshiped the beast or his statue, nor accepted his mark on their foreheads or their hands. They all came to life again, and they reigned with Christ for a thousand years.
This is the first resurrection. (The rest of the dead did not come back to life until the thousand years had ended.)
Blessed and holy are those who share in the first resurrection. For them the second death holds no power, but they will be priests of God and of Christ and will reign with him a thousand years.