A.T. Robertson Commentary Revelation 19:5

"And a voice came forth from the throne, saying, Give praise to our God, all ye his servants, ye that fear him, the small and the great." — Revelation 19:5 (ASV)

A voice from the throne (φωνη απο του θρονου). Not the voice of God, nor of the Lamb, nor εκ του ναου (16:17), but from an angel of the Presence. This angel summons all the servants of God to join in the antiphonal praise to God.

Give praise to our God (αινειτε τω θεω ημων). Present active imperative of αινεω, old verb, with the accusative elsewhere in N.T., but here with the dative as occasionally in the LXX (1 Chronicles 16:36, etc.).