Revelation chapter 15 begins the preparation for the last seven vials. The wrath of God began with the seven seals (in chapter 6), and will be finished with the last seven vials. Chapter 15 is an introduction to these last seven and final plagues on mankind.
After the trumpet judgments, the focus of Revelation changed from a more-or-less chronological account to a description of certain people and events. Among these are infamous concepts such as the woman clothed with the sun, the Antichrist, the False Prophet, and the mark of the beast. Here, John will see one final vision before he is shown the rest of the tribulation judgments, represented by bowls.
The first vision John sees here is that of seven angels. These carry the last judgments God will use during the tribulation. The scene is one of celebration, as redeemed believers sing a song of worship to God. The sea of glass mentioned here is presumably the same one referred to in Revelation 4.
Revelation presents God's final judgments on sin in three groups of seven. The first set of judgments was represented by the opening of seals on a scroll (Revelation 5:1). The second set was represented by trumpets (Revelation 8:6). This last pattern will involve bowls, symbolically filled with the wrath of God. This segment also indicates that the sanctuary in heaven was filled with smoke during this time, preventing anyone from approaching God until the judgments were completed (Revelation 15:5–8).
Throughout history God has poured out his wrath in judgment on early sinners. Adam's sin in the Garden of Eden brought the entire human race under judgment. By Noah's days, people had turned so wicked, that God sent the judgment of the flood to destroy the entire world except eight people, Noah, his three sons and their wives.
Centuries of disobedience and wickedness by the Jewish people eventually led to their judgment and captivity. First the northern 10-1/2 tribes (in 722 B.C.), by the Assyrian Empire. Then the southern kingdom of Judah (in 586 B.C.), by the Babylonian Empire.
Now in Chapters 15 and 16 we see the final outpouring of God's wrath before Christ's return.
What a terrible thing it is to fall into the hands of the Living God and be judged by Him guilty and deserving of His wrath.
1 And I saw another sign in heaven, great and marvelous, seven angels having the seven last plagues; for in them is filled up the wrath of God.
2 And I saw as it were a sea of glass mingled with fire: and them that had gotten the victory over the beast, and over his image, and over his mark and over the number of his name, stand on the sea of glass, having the harps of God.
(They stand on that sea of glass (transparency before God) mingled with fire (testings and tribulations of earthly life.)
(Having come through the flames of adversity, those standing upon the sea of glass have been refined (1Pe. 1Pe. 1:7; 1 Pe. 4:12). The allotted number of martyrs is complete, and God will finish His vengeance.
3 And they sing the song of Moses the servant of God, and the song of the Lamb, saying, Great and marvelous are thy works, Lord God Almighty; just and true are thy ways, thou King of saints.
4 Who shall not fear thee, O Lord, and glorify thy name? for thou only art holy: for all nations shall come and worship before thee; for thy judgments are made manifest.
5 And after that I looked, and, behold, the temple of the tabernacle of the testimony in heaven was opened.
The tabernacle (in ancient times) was a portable place of worship God commanded the Israelites to build after he rescued them from slavery in Egypt. It was used from a year after they crossed the Red Sea until King Solomon built the first temple in Jerusalem.
(Whatever is about to come forth from the temple is a manifestation of God’s judgment for those who fall short of the testimony (witness) of the law and who have not sought Christ for refuge from God’s wrath.)
6 And the seven angels came out of the temple, having the seven plagues, clothed in pure and white linen, and having their breasts girded with golden girdles.
7 And one of the four beasts gave unto the seven angels seven golden bowls full of the wrath of God, who liveth for ever and ever.
(The wrath contained in these bowls represents God’s response to the mountains of prayers over the ages by the saints of God to avenge the blood of the martyrs (Rev. Rev. 6:10+) and to bring His kingdom to earth (Mtt. Mat. 6:10; Luke Luke 18:7-8.)
8 And the temple was filled with smoke from the glory of God, and from his power; and no man was able to enter into the temple, till the seven plagues of the seven angels were fulfilled.
Summary: John saw the seven angels having the seven last plagues wherein the wrath of God is complete (Rev. Rev. 15:1+). He was also shown those who had overcome the Beast and had refused to worship him or take his mark. These were undoubtedly martyred, filling up the cup of God’s wrath even further. The angels have been given the seven bowls of the wrath of God, and God has shut Himself within the Temple to be alone, undisturbed during the pouring forth of the bowls.