Whatever they make of the blowing of the seventh trumpet most commentators judge it to something that was future at the time John was writing the book of Revelation. I'm interested particularly in Revelation 11.15-17 which says this (NIV):
" 'The kingdom of the world has become the kingdom of our Lord and of his Christ, and he will reign for ever and ever.' And the twenty-four elders, who were seated on their thrones before God, fell on their faces and worshiped God, saying, 'We give thanks to you, Lord God Almighty, who is and who was, because you have taken your great power and have begun to reign.' "
All the other versions agree with the sense given by the NIV in 11:17 that the Lord God Almighty took his great power and began to reign. The ingressive first aorist is in the indicative (ebasileusas) and follows God's act of taking his power. Of that a perfect is used (eleiphes), which in association with the finality of the reign of Jesus probably speaks of permanence; that is, God at this point once and for all took his power and began to reign.
This raises a series of questions only two of which I'm interested in here:
1) What does it mean that God "took his great power"?
2) How does it come that he "began" to reign at this point?
Both phrases seem to suggest that God was without power or kingly sovereignty prior to the blowing of the 7th trumpet. That impression is only a surface one and it is incorrect. God has never been without power and his kingly rule is unbroken from eternity to eternity.
For our purposes here it doesn't matter to me whether one believes that the 7th trumpet is sounded at the end of human history or at 70AD or any other date after the appearance of Jesus Christ. My own view is that it speaks of God's judgement on the Roman Empire as it is represented by the emperor Domitian; but for now that is of no consequence. What are we to make of the claim that at the sound of the 7th trumpet God "took his great power" and "began to reign"?
Since the Bible everywhere insists that God reigns without limit over all that there is and has always so reigned and will always so reign, how are we to understand the two phrases?
We are to take it that these are specific manifestations of that already existing power and royal sovereignty. The power God always had simply by virtue of his being God was exercised in a specific way. Whatever we make of the event(s) in view in the 7th trumpet it was not at that moment that God became Almighty or gained his almighty power. It was at that time that God expressed or showed or exhibited his almighty power.
Let's say we know beyond dispute what the 7th trumpet sounding meant. Let's call it X. The passage says that at X God took his great power and used it in a certain way to gain a certain object.
That act of God—his taking his almighty power—is further explained in the phrase "and began to reign." The idea that God had not already been reigning prior to X makes no biblical sense at all. It would certainly make sense if we were to say that God began to reign through a certain individual at X or that he began to exercise his dominion in a certain way, a way in which he hadn't been exercising it before or that he was publicly exhibiting his already existing reign. All those would make sense but to say that God was not reigning prior to X makes no sense! Bless me, nothing can exist or continue to exist if God doesn't enable it to exist (Revelation 4:10-11) so how can he be without power or royal sovereignty at any point?
So what is the passage not saying? The passage is not saying that God was without controlling power or kingly sovereignty prior to the sounding of the 7th trumpet. Yes, but the passage does say he began to reign at the sound of the 7th trumpet. This is true but we're faced with a choice between an actual beginning of the reign of God or a particular expression of the reign of God and there's no doubt in my mind which we are to go for.
11:15 tells us that at this point "the kingdom of the world" has become the kingdom of the Lord (and of his Christ). The empire that expressed the world spirit at this time was Rome (Revelation 17:9, 18) in keeping with Daniel 2 and 7. He who established these kingdoms on the earth (Babylon—Rome) promised that he would come in judgement on that four-fold structure and smite it in its Rome phase (be sure to see Daniel 2:31-45 and 7:1-27).
God's judgement on Rome was the public demonstration of God's sovereignty and not its beginning. It was God who raised up Rome (compare Daniel 4:17 with 2:37 and 7:2 with the wind as divine stirring) and when he judged her he was expressing the same sovereign power that he showed when he raised her up. So when we're told that the kingdom of the world has become the kingdom of the Lord we're not to be fooled into thinking that it wasn't already under God's sovereign power. He did then what psalmists of old asked him to do over and over again when they asked deliverance from their enemies. They asked God to show his sovereign power over the nations. That's what happens in Revelation 11:15-17 in light of 6:9-11 and see 18:20 when the city of Rome is seen to be destroyed.
And as surely as we are not to think that God's reign over Rome began with Revelation 11:15-17 we are not to think Jesus' reign began at 11:15-17. Jesus had already been made Lord of All (Acts 2:36, Ephesians 1:19-22; 1 Peter 3:21-22; Philippians 2:9-11, and everywhere else) prior to the writing of the book of Revelation. But who believed it at the beginning? Rome and the nation of Israel had conspired against the Lord and his Christ (see Psalm 2:1-9 and Acts 4:25-28) but failed to keep Jesus off the throne of the universe under God. For their pains and in demonstration of their failure God judged both Israel and Rome. See the above link.
The 7th trumpet in Revelation 11, as you will notice, contains the 7 bowls (as the 7th seal contained the 7 trumpets) and the seven bowls are the full outpouring of the plagues of God on the Roman Empire (the images are taken from the plagues poured out on Egypt at which time God was vindicating his "son"—Israel, and confirming his reign over Egypt and the world). Rome that claimed to be the divine city and persecuted the city of God (the people of God) claimed universal dominion and God in judging her made a public proclamation that he had universal dominion and that he had invested it his Son, Jesus the Christ. 11:15-17 teaches us that what was already true was publicly demonstrated when God exercised his almighty power and made his sovereignty visible.