This "SEA OF GLASS" is the same "Sea of Glass" that we saw before the Throne in chapter 4:6. Then it was unoccupied, now it is occupied. Then its surface was crystal clear and plain, now its surface is of a "fiery" aspect, symbolizing the "fiery trials" of its occupants. The occupants of this "Sea of Glass" come out of the Great Tribulation, for they have gotten the victory over the "Beast," and over his "Image," and over his Mark, and over the "Number of His Name," and they have harps, and they sing the "SONG OF MOSES" and the "SONG OF THE LAMB." They are the "Harpers" of chapter 14:2, whose song only the 144,000 "Sealed Ones" could sing. John only heard them then, now he sees them. That they could sing both the "Song of Moses" and the "Song of the Lamb" implies that they were all or in part Israelites. Some think that the "Song of Moses" that they sung was the song the Children of Israel sang on the shore of the Red Sea after their escape from Egypt, as given in Ex. 15:1-22, while others think it is Moses' "SWAN SONG" as found in Deu. 31:19, 22; 31:30; 32:43. They sang the "Song of the Lamb" because as Israelites they had been redeemed by the blood of the Lamb.