Revelation 15:1 "And I saw another sign in heaven, great and marvellous, 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. 3 And they sing the song of Moses the servant of God, and the song of the Lamb, saying, Great and marvellous 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: 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 vials full of the wrath of God, who liveth for ever and ever. 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."
Fourth and final account of the Tribulation
15:1 - The Tribulation saints are probably gone when these events take place. The Beast starts to give his Mark in the Middle of the Tribulation (Revelation 13). The vials are poured out at the last half of the Tribulation.
15:2 - This verses shows that there is a Tribulation Rapture. These people match the ones in Revelation 14:2-3, 4:6 and 7:13-15. This event takes place before the Second Advent. The sea of glass is talked about in Job 37:10,18, 38:30 and Revelation 4:6.
15:3 - The song of Moses is mentioned in Deut. 32:1-44. This shows that Deut. 32 was not fulfilled at the First Coming, so it will be fulfilled in the Second Coming. This verse shows a faith and works set up in the Tribulation because of the songs mentioned, the song of Moses(law) and the Lamb(faith). Jesus Christ is the head of the Body of Christ, but will not be King until the Second Advent.
15:4 - This is a reference to the Second Advent. Cross references: Zechariah 14:16-17, Isaiah 2:1-4, 60:14, 62:7, Micah 4:1-2, Ezekiel 48:35, Jeremiah 3:17, Psalms 2:6-12, 66:4, 72:11, 86:9, 110:2, 96, 97
15:5-8 - The temple is found in heaven (Revelation 14:17, 11:19, 8:3-5). These last plagues will fall on those who reject Jesus Christ towards the end of the Tribulation.