He sees seven angels having seven vials full of wrath.

15 And I saw another sign in heaven, great and marvellous: seven angels having the seven last plagues. For in them is fulfilled the wrath of God. ² And I saw as it were a glassy sea mingled with fire, and those who had gotten the victory of the beast, and of his image, and of his mark, and of the number of his name, standing on the glassy sea, having the harps of God. ³ And they sang the song of Moses, the servant of God, and the song of the Lamb, saying, Great and marvellous are your works, Lord God Almighty! Just and true are your ways, King of saints! ⁴ Who would not fear, O Lord, and glorify your name? For you alone are holy, and all the Gentiles will come and worship before you, for your judgments are made manifest.

⁵ And after that I looked, and behold, the temple of the tabernacle of testimony was open in heaven. ⁶ And the seven angels that had the seven plagues came out of the temple, clothed in pure and bright linen, and having their breasts girded with golden girdles. ⁷ And one of the four living creatures gave to the seven angels seven golden vials full of the wrath of God, who lives forevermore. ⁸ And the temple was full of the smoke of the glory of God and of his power, and no one was able to enter into the temple till the seven plagues of the seven angels were fulfilled.