A.T. Robertson Commentary Revelation 4:6

"and before the throne, as it were a sea of glass like a crystal; and in the midst of the throne, and round about the throne, four living creatures full of eyes before and behind." — Revelation 4:6 (ASV)

As it were a glassy sea (ως θαλασσα υαλινη). Old adjective (from υαλος, glass, 21:18,21), in N.T. only here and 15:2. Possibly from υε (it rains), like a raindrop. At any rate here it is the appearance, not the material. Glass was made in Egypt 4,000 years ago. In Ex 24:10 the elders see under the feet of God in the theophany a paved work of sapphire stone (cf. Ezekiel 1:26). The likeness of the appearance of sky to sea suggests the metaphor here (Beckwith).

Like crystal (ομοια κρυσταλλω). Associative-instrumental case after ομοια. Old word, from κρυος (ice and sometimes used for ice), in N.T. only here and 22:1, not semi-opaque, but clear like rock-crystal.

In the midst of the throne (εν μεσω του θρονου). As one looks from the front, really before.

Round about the throne (κυκλω του θρονου). Merely an adverb in the locative case (Romans 15:19), as a preposition in N.T. only here, 5:11; 7:11. This seems to mean that on each of the four sides of the throne was one of the four living creatures either stationary or moving rapidly round (Ezekiel 1:12f.).

Four living creatures (τεσσερα ζωα). Not θηρια (beasts), but living creatures. Certainly kin to the ζωα of Eze 1; 2 which are cherubim (Ezekiel 10:2,20), though here the details vary as to faces and wings with a significance of John's own, probably representing creation in contrast with the redeemed (the elders).

Full of eyes (γεμοντα οφθαλμων). Present active participle of γεμω, to be full of, with the genitive, signifying here unlimited intelligence (Beckwith), the ceaseless vigilance of nature (Swete).