Literally, of course, the sea cannot mingle with fire. But repeatedly throughout Scripture the presence of God is indicated with fire (Genesis 15:17; Exodus 3:2; Exodus 19:18; Judges 6:21; Acts 2:3). The presence of fire upon/through this floor indicated the presence of God. In fact, the emphasis on wrath and bowls in the course of this chapter will make clear why God’s presence is indicated by fire.
2 And I saw what appeared to be a sea of glass mingled with fire and also those who had conquered the beast and its image and the number of its name, standing beside the sea of glass with harps of God in their hands.