The ESV says that the redeemed were standing “beside the sea of glass.” That would make sense if the “sea” were something like the bath of Solomon’s temple (1 Kings 7:23). The Greek preposition used, however, means “upon”—as we expect when we understand that John uses the phrase “a sea of glass” to describe the floor under God’s throne. These triumphant saints are standing in God’s very presence.
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.