The Sea of Glass
“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.”
(Rev 15:2-4 KJV)
The sea of glass was seen in chapter 4 before the throne of God.
“And before the throne there was a sea of glass like unto crystal: and in the midst of the throne, and round about the throne, were four beasts full of eyes before and behind.” (Rev 4:6 KJV)
Now we see the sea of glass mingled with fire and the martyrs that were killed by the antichrist. They overcame his persecution and did not worship his image or take his mark.
They were given harps and sing praises to God – the song of Moses and the song of the Lamb – both songs of victory and praise to God.