And the seventh angel sounded...
The things associated with this angel have to do with the announcement that the change of power is complete, that the earth is now under the control of King Jesus and His Church. Once again, Biblical numerology comes to play. The number "7" means final, complete, the ultimate; and the Lord's Millennial kingdom surely satisfies the meanings of the number. In Revelation 4:11 we read: "Thou art worthy, O Lord, to receive glory and honour and power: for thou hast created all things, and for thy pleasure they are and were created." So during the Kingdom Age, the world will complete its reason for being created. The Millennium will also satisfy the concept of finality in that His kingdom will be established in the final age or dispensation of time — in fact, it will rule for the duration of the the final age. This is why His kingdom is also labeled as the 1,000 years of peace. In addition, the Millennium will surely satisfy the meaning of ultimate; for the world will finally realize its full potential as the Son of God nurtures His creation into full bloom.

...and there were great voices in heaven... According to Strong's Lexicon, the word great has at least two basic meanings:
(1) powerfully affecting the senses: violent, mighty, strong; and
(2) predicated of rank, as belonging to
a) persons, eminent for ability, virtue, authority, power
b) things esteemed highly for their importance: of great moment, of great weight, importance
c) a thing to be highly esteemed for its excellence: excellent
As we think on these great voices, lets go to Mat 5:19:
"Whosoever therefore shall break one of these least commandments, and shall teach men so, he shall be called the least in the kingdom of heaven: but whosoever shall do and teach [them], the same shall be called great in the kingdom of heaven."
This being so, then surely as the glorified Church in heaven raise their voices in praises, hallelujahs, and amens, they will satisfy both meanings of the term great voices!
...saying, The kingdoms of this world are become the kingdoms of our Lord... There is so much that our finite minds cannot grasp. Here, at last, Christ will get the kingdoms that the devil tried to bribe Him with during His temptation in the wilderness.

(Mat 4:8-9)
Again, the devil taketh him up into an exceeding high mountain, and sheweth him all the kingdoms of the world, and the glory of them;
And saith unto him, All these things will I give thee, if thou wilt fall down and worship me.

During His Visitation, When the Lord disrobed Himself of His glory and came to the earth as a man, we cannot know just how much of His divinity He chose to retain and how much He chose to lay aside for a moment in time. If He was fully aware of Who He was and what He was about at the time of His temptation, would the temptation have had any significance? As I say, we cannot know, but we can know — Thank God — that it won't be long before the kingdoms of the world will become the Lord's to rule. (Even now, only He can straighten out the mess that man has made of things.)

...and of his Christ... We're dealing here with the Trinity, another of those mysteries that belong to the Lord. As it was during His Visitation, God the Father (Who is a Spirit) will once again send His Only Begotten Son (the Christ) to do a work on His earth — only this time He will come in a glorified body to rule the earth with a rod of iron. And take heart, Church, for Christ Jesus will not come by Himself, but He will bring you and I with Him; and we, too, will have our glorified bodies at the time.

...and he shall reign for ever and ever. Thank God that this is so, for only He is worthy to do so; and think about it, only He is able to do so!

And the four and twenty elders... This is a prophetic, representative term assigned to the glorified Church in heaven.
... which sat before God on their seats... This will be our normal state in heaven; i.e., occupying before God the positions assigned us. By this time we will be "over the angels" and we will have already been co-rulers with Christ on the earth.

(I Corinthians 6:1-3)
Dare any of you, having a matter against another, go to law before the unjust, and not before the saints?
Do ye not know that the saints shall judge the world? and if the world shall be judged by you, are ye unworthy to judge the smallest matters?
Know ye not that we shall judge angels? how much more things that pertain to this life?

...fell upon their faces... In this life we fall on our faces in contrition, humbling ourselves before our God and repenting of the hated sins of our tainted flesh. However, in heaven there will be times when we will spontaneously fall on our faces before the awesome God Who made us — Who made all things for us — and Who died the unfathomable death of the cross so that we might be able to choose to enter into those things that He made for us.

...and worshipped God. We admire our peers who do well, we love our neighbors and our families, we adore our spouses; and all these affections are expressed in different ways. But worship is the spontaneous, joyful way we in the Church (the apple of God's eye) express our love and delight to the One Who saved us and Who has set us up in heavenly places. As per this verse, however, the saints will already know as they are known and they will fully comprehend what Christ did for them. Consequently, worship will have new meanings and it will find new depths.

17 Saying, We give thee thanks, O LORD God Almighty, which art, and wast, and art to come; because thou hast taken to thee thy great power, and hast reigned.

Saying, We give thee thanks, O LORD God Almighty... In general, mankind teaches their children to be thankful to one another and to express their graduated towards each other; yet they have no desire to thank their Creator for all that they are and all that they have. The only explanation for this is that in his fallen state, man is dead to God and has no desire to recognize Him. This is why Jesus told Nicodemus, a ruler of the Jews in His day, that to enter into the kingdom of God he must be born again. For those who have thus been born again, thankfulness to God is as natural as breathing.

...which art, and wast, and art to come... Once again, this is a descriptive title that belongs to the risen Christ, and to Him alone. As we can see from the rest of this verse, it is not a chronological key.

...because thou hast taken to thee thy great power, and hast reigned.   This is the chronological key. They are praising the Christ who has already reigned as King of the earth for the duration of the Millennium.

18 And the nations were angry, and thy wrath is come, and the time of the dead, that they should be judged, and that thou shouldest give reward unto thy servants the prophets, and to the saints, and them that fear thy name, small and great; and shouldest destroy them which destroy the earth.

This verse is chock full!
And the nations were angry... Notice the past tense: "were angry." Again, the Kingdom Age is past. This attitude of the people brings to mind a similar situation during the time of our Lord's Visitation. For three years Jesus walked the earth among men and women and demonstrated via love and power Who He was and What He was about, yet the majority of the people rejected Him and His claim on their lives.

In the accounts given in the New Testament, it seems that the leaders of the Jews would have accepted Christ had He lined up with their goals and ideas. So, maybe the greater majority of the people did not accept Christ because He would not fit into their agenda and He wouldn't change His agenda to fit theirs. Jesus did leave us some insight into this mystery in John 3:16-19.

For God so loved the world, that he gave his only begotten Son, that whosoever believeth in him should not perish, but have everlasting life.
For God sent not his Son into the world to condemn the world; but that the world through him might be saved.
He that believeth on him is not condemned: but he that believeth not is condemned already, because he hath not believed in the name of the only begotten Son of God.
And this is the condemnation, that light is come into the world, and men loved darkness rather than light, because their deeds were evil.

So be it for selfishness or evil deeds — from the Scriptures it doesn't look like there's much difference in the two — man has chosen to reject his Maker. Here again during the Kingdom Age, we see Christ walking among the men and women He Created and died for, only to once again be reject by many of them. And once again we see what seems to be an inexplicable anger in those who reject the Son of God.

...and thy wrath is come... But not only will the nations be angry, but this time, Christ will not submit Himself dumb as a lamb to man's inhumane ways. Rather, He will show that He is also capable of anger. And as we've already seen in our study, at this point He will have already been pouring His wrath out upon the rebellious inhabitants of the earth for some time.

...and the time of the dead, that they should be judged... Another clue as to the time. The dead shall be judged at the Great White Throne Judgment at the end of the Kingdom Age (Rev. 20:11).

...and that thou shouldest give reward unto thy servants the prophets, and to the saints, and them that fear thy name, small and great... Since those who lived and served God prior to the Kingdom Age received their rewards at the Judgment Seat of Christ right after the Rapture of the Church, this is probably referring to the rewards that will be given at the end of the Kingdom Age to those who lived and served God during the Millennium.

...and shouldest destroy them which destroy the earth. It is easy to recognize Satan's tracks. If he can't have his way, he'll just destroy everything. However, it is now time for the destroyer and all who adopted his ways to be destroyed.

19 And the temple of God was opened in heaven, and there was seen in his temple the ark of his testament: and there were
lightnings, and voices, and thunderings, and an earthquake, and great hail.

And the temple of God was opened in heaven... This is another verse that is loaded with meaning. The temple of God is, of course, Christ Jesus; and since the Church is grafted into Him so that they are one, then this temple would be Christ Jesus and His glorified Church. (cf. I Cor. 6:19: "What? know ye not that your body is the temple of the Holy Ghost which is in you, which ye have of God, and ye are not your own?" cf. I Peter 2:5) Also, this temple is the anti-type of the Jewish temples which pointed forward to Christ as per God's promises to Father Abraham — and as such, it is another reminder to Abraham's seed and to the world, that God has not forgotten His promises to Abraham.
In addition, that the temple is opened for the world to see brings to mind the account of the rich man and the beggar Lazarus in Luke 16:22-31. (Those who are not familiar with the account should read it now.) The rich man was a pious Jew who had no time or thought for the plight of the beggar Lazarus. His hypocrisy earned him a place in hell, and Jesus said of the rich man: "And in hell he lift up his eyes, being in torments, and seeth Abraham afar off, and Lazarus in his bosom." Seeing Lazarus being comforted in Abraham's bosom was part of the rich man's torment. Likewise, the ungodly on the earth who have chosen to rebel against the Son of God will get to see the believers that they despised on the earth tasting the goodness of God in heaven while they know fear and torment.

...and there was seen in his temple the ark of his testament... In the Old Testament, the ark typifies the presence of Christ. Consequently, just as the temple is representative of Christ and the Church in the New Testament, so is the ark representative of Christ and the nation Israel in the Book of Revelation.

...and there were lightnings, and voices, and thunderings, and an earthquake, and great hail. Again, these are prophetic terms associate with the judgment of God. It is also possible that they should also be interpreted literally and that God is using the things of nature as a part of his judgment upon those who would destroy His earth.