The voice comes from near the throne. It is not the voice of God Himself, as indicated by what is said: Praise our God. It is probably the voice of an angel of high rank, such as one of the living creatures.
Praise our God all you His servants
Praise is αἰνεῖτε [aineite] , second person, plural, imperative command: you all praise! You who fear the LORD, praise Him! All you descendants of Jacob, glorify Him, and fear Him, all you offspring of Israel (Ps. Ps. 22:23). Many of those who praise are the very servants whos blood was shed by the Harlot (Rev. Rev. 19:2+). They praise all the more because God has avenged their martyrdom. Having experienced greater depths of persecution, they have greater ability to extol and elevate God.
Behold, bless the LORD, all you servants of the LORD, who by night stand in the house of the LORD! Lift up your hands in the sanctuary, and bless the LORD. The LORD who made heaven and earth bless you from Zion! (Ps. Ps. 134:1-3)
Praise the LORD! Praise the name of the LORD; praise Him, O you servants of the LORD! You who stand in the house of the LORD, in the courts of the house of our God, praise the LORD, for the LORD is good; sing praises to His name, for it is pleasant. (Ps. Ps. 135:1-3)and those who fear Him, both small and great!
Some manuscripts omit and (καὶ [kai] ). If included, it should probably be translated as even since the clause which follows provides additional description of the servants and does not denote a separate category of persons. Fear of God is an important aspect of understanding Who He is (Acts Acts 10:2). See commentary on Revelation 11:18. The company of the redeemed knows no boundaries and includes those who have had considerable influence and power in life, as well as those who are entirely unknown to the world. The cross of Christ is the great equalizer among men.