John saw another great sign in heaven: seven angels with the seven last plagues; these are the last plagues in that with them God’s wrath would be completed or fully expressed. This is the third great sign that John saw - the first was the woman (12:1) and the second was the great red dragon (12:3).
Then standing beside the sea of glass glowing with fire were the overcomers - those who had been victorious over the beast and its image and over the number of its name (15:2 cf., 12:11) - those who were killed because they refused to worship the beast and its image and those who died of starvation rather than be marked by the number of the beast. Paradoxical but their victory was achieved by their death. These martyred dead held harps and sang the song of Moses and of the Lamb (15:3-4).
John saw that the temple in heaven (the tabernacle of the testimony) was opened. Out of it came the seven angels with the seven plagues, dressed in shining linen with golden sashes around their chests (15:5-6).
Then one of the four living creatures gave to the seven angels seven golden bowls filled with the wrath of God (15:7).
The temple was filled with smoke from the glory of God and from His power, and no one could enter the temple until the seven plagues were poured out and completed (15:8).
"The major problem is how a war is possible when there is a world government under the control of Satan and the beast. Some have interpreted this as a gathering of forces in anticipation of the second coming of Christ. More probably, it reflects a conflict among the nations themselves in the latter portion of the great tribulation as the world empire so hastily put together begins to disintegrate. The armies of the world contending for honors on the battlefield at the very time of the second coming of Christ do all turn, however, and combine their efforts against Christ and His army from heaven when the glory of the second coming appears in the heavens. It will be the final challenge to divine sovereignty and power as the military might of the world of that day will be engaged in fighting on the very day that Christ returns (cf. Zech. 14:1-3). It is significant that the battle itself bears the name of “that great day of God Almighty.” (Source: John Walvoord in The Vials Of The Wrath Of God)