Revelation 16 reveals God's judgment on the world through the 7 bowl judgments. The words "It is done!" appear at the end of this chapter, and indeed the world is poised to destroy the nation of Israel at one last battle.
Chapter 15 presents and incredible scene of God's glory and justice. We see all those martyred in the tribulation playing harps givens to them by God Himself.
This is one of the darkest chapters in the Bible (imo). If the fall of man (Genesis 3) and the crucifixion (John 15) were the epitome of sadness for God the Father, then this surely must be just as difficult.
Judgment on the earth, Israel and Christians begins in earnest. During the last 3 1/2 years of the tribulation, it's a death sentence if you identify with Christ. Yet untold numbers will!
The most amazing statement occurs in Revelation 12:10.
“Then I heard a loud voice shouting across the heavens, “It has come at last— salvation and power and the Kingdom of our God, and the authority of his Christ. For the accuser of our brothers and sisters has been thrown down to earth— the one who accuses them before our God day and night.”
Revelation 12:10 NLT
Salvation, power, the Kingdom of God and the authority of Christ have finally come together! History is coming to a close and all the promises are being fulfilled in completeness.
Revelation 12-15 are a parentheses in the seven year timeline. The 7th trumpet is sounded in chapter 11, but we don't see the events it produces until chapter 16.
In Chapter 12 we're introduced to 7 "personages" - see the notes.
The world has never seen two men quite like this. They preach the gospel, call down judgment, reign down plagues on all of mankind by their own command. After three and a half years they are killed by the Antichrist and their bodies lie in the streets of Jerusalem for three and half days. But that's not where the story ends.