Charles Ellicott Commentary Revelation 16:7

"And I heard the altar saying, Yea, O Lord God, the Almighty, true and righteous are thy judgments." — Revelation 16:7 (ASV)

And I heard . . .—Translate, And I heard (not “another out of the altar,” but) the altar saying, Even so, Lord God the Almighty, true and righteous are Your judgments. The altar beneath which the souls of the martyrs cried, and on which the prayers of saints were offered, is represented as confirming the testimony to the just dealings of God.