And I saw as it were a sea of glass mingled with fire. "And I saw" indicates a new phase of the vision (cf. Revelation 14:6, Revelation 14:14, etc.). The sea was like glass, either because of its pure transparent appearance, or on account of its consistency; the saints being subsequently described as standing on it.
(For a full discussion of the meaning, see on Revelation 4:6.) The sea, the elders, and the triumphal hymns of praise are all characteristic of the vision in Revelation 4:1-11. Mingled with fire. In Revelation 4:1-11.
it was described as "like unto crystal." The fire is an emblem of purity; the same idea is also conveyed by the "crystal." Fire is also a symbol of judgment, which is the theme of the song of the saints (Revelation 4:4).
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; and them that come victorious from the beast and from his image, and from the number, etc.
Omit "and over his mark," according to all the best authorities. Standing by (or, on), having harps. (On "the beast" and "his image," etc., see on Revelation 13:1-18.) These victorious ones stand by (such, probably, is the force of ἐπί) the sea (see above and on Revelation 4:6).
The "harps" are characteristic of the heavenly melodies (Revelation 5:8; Revelation 14:2). This multitude has been before described in Revelation 7:9. From his image; that is, from the temptation to worship the image.