20 And I saw an angel coming down out of heaven, having the key to the Abyss and holding in his hand a great chain.

2 He seized the dragon, that ancient serpent, who is the devil, or Satan, and bound him for a thousand years.

bound him for a thousand years. This number is symbol of a long, complete yet temporal period. 10 X 10 X 10 =1,000. The word “bound” was used by Jesus to describe Satan’s “defeat” at the cross (Matt 12:29). Satan is bound not annihilated. He is still around but his powers have been legally broken. Other sincere and committed Christians believe the 1,000 years take place after the return of Christ.

3 He threw him into the Abyss, and locked and sealed it over him, to keep him from deceiving the nations anymore until the thousand years were ended. After that, he must be set free for a short time.

to keep him from deceiving the nations anymore. Satan’s greatest strength is deception. His powers of deception are hindered. All Nations may now receive the gospel as a testimony (Matt 24:14).

he must be set free for a short time. A reminder that at the end there will be an apostasy. Thankfully the apostasy will not last as long as world evangelization.

4 I saw thrones on which were seated those who had been given authority to judge. And I saw the souls of those who had been beheaded because of their testimony for Jesus and because of the word of God. They had not worshiped the beast or his image and had not received his mark on their foreheads or their hands. They came to life and reigned with Christ a thousand years.

They came to life. We were dead in our transgressions and sins, and now we are alive spiritually (Eph 2:5-6).

5 (The rest of the dead did not come to life until the thousand years were ended.) This is the first resurrection.

This is the first resurrection. Those who believe in a pre-tribulation rapture will have to explain how the so called “tribulation saints” were resurrected after the tribulation, and yet this is called the first resurrection. Wouldn’t the first resurrection be the one before the tribulation? In my view, the first resurrection is the spiritual one called the new birth. See v 4.

6 Blessed and holy are those who have part in the first resurrection. The second death has no power over them, but they will be priests of God and of Christ and will reign with him for a thousand years.

Blessed and holy are those who have part in the first resurrection. According to the Strong's Concordance, the word “have” (gr. echo) is “used in certain tenses only; a primary verb, to hold.” John is saying that blessed and holy are those who “right now, currently hold onto” the first resurrection. In other words, John does not see the first resurrection as a future blessing of the believer, but a current one, which could only refer to the spiritual resurrection from sin. If he had meant a physical future resurrection (which we do anticipate) he would have said, “Blessed and holy are those who WILL have part in the first resurrection.”

7 When the thousand years are over, Satan will be released from his prison

When. Literally “whenever”. This shows that the completion of 1,000 years is not exact.

Satan will be released from his prison. This goes along to what we have already noted in the book, that there will be a last day apostasy.

8 and will go out to deceive the nations in the four corners of the earth — Gog and Magog — to gather them for battle. In number they are like the sand on the seashore.

will go out to deceive the nations. Nations that owe its prosperity to the gospel of Christ will turn against it. Perhaps we are seeing the beginning of this deception.

Gog and Magog. The old nations that warred against Israel (Ez 38). Just as Israel was the people of God under the Old Covenant we are the people under the New Covenant and we will face a spiritual battle at the end.

In number they are like the sand on the seashore. Apparently they will outnumber the followers of Christ.

9 They marched across the breadth of the earth and surrounded the camp of God's people, the city he loves. But fire came down from heaven and devoured them.

surrounded the camp of God's people, the city he loves. The city here is the New Jerusalem. We will find ourselves outnumbered and out maneuvered. 

fire came down from heaven and devoured them. When it looks like we are defeated, the Lord returns.

10 And the devil, who deceived them, was thrown into the lake of burning sulfur, where the beast and the false prophet had been thrown. They will be tormented day and night for ever and ever.

thrown into the lake of burning sulfur. The ultimate purpose for God creating eternal fire was for the devil and his angels (Matt 25:41).

where the beast and the false prophet had been thrown. The beast and false prophets as well as everyone who rejected Christ will find their eternal destiny to be the same as the devil. 

11 Then I saw a great white throne and him who was seated on it. Earth and sky fled from his presence, and there was no place for them.

12 And I saw the dead, great and small, standing before the throne, and books were opened. Another book was opened, which is the book of life. The dead were judged according to what they had done as recorded in the books.

books were opened. Imagine someone keeping track in a book of everything you do, say and think. This is the picture John gives of every soul.

Another book was opened, which is the book of life. If it wasn’t for “another book” we would all be doomed. Thankfully there is a book of life that one can have his name inscribed in by accepting Christ.

The dead were judged according to what they had done. Sinners cannot argue that they are judged simply because they did not accept Christ; they will be judged according to their deeds. Unfortunately for them, their deeds will never earn their way to eternal life. 

13 The sea gave up the dead that were in it, and death and Hades gave up the dead that were in them, and each person was judged according to what he had done.

judged according to what he had done. See v 12.

14 Then death and Hades were thrown into the lake of fire. The lake of fire is the second death.

The lake of fire is the second death. The first death is “separation from God because of sin.” The sinner is now dead because of sins.

15 If anyone's name was not found written in the book of life, he was thrown into the lake of fire.

Clearly no one will be found worthy to avoid the lake of fire through righteous acts.