I saw in heaven another great and marvelous sign: seven angels with the seven last plagues — last, because with them God’s wrath is completed. 2 And I saw what looked like a sea of glass mixed with fire and, standing beside the sea, those who had been victorious over the beast and his image and over the number of his name.
Here, as John sees the last plagues coming (v. 1)—which will finish the wrath of God—he then sees the victorious ones in heaven, rejoicing in their victory over the beast and in the greatness of God.
They will sing the song of Moses (Ex. 15:1-21), which the people of Israel sang after they passed through the Red Sea; and they will also sing the song of the Lamb (Rev. 5:8-14), which is their rejoicing in the blood of Christ to redeem them from sin.
Verses 3 and 4, I think, is a short condensation of the song of Moses and the Lamb, and is the high points of what will be their worship to God and to the Lamb. In these verses they extol His greatness and holiness and sing of His future millennial reign in the new kingdom when “all the nations will come and worship before [Him].”
They held harps given them by God 3 and sang the song of Moses the servant of God and the song of the Lamb:
“Great and marvelous are your deeds,
Lord God Almighty.
Just and true are your ways,
King of the ages.
4 Who will not fear you, O Lord,
and bring glory to your name?
For you alone are holy.
All nations will come
and worship before you,
for your righteous acts have been revealed.”