And the sixth angel sounded,.... His trumpet:and I heard a voice from the four horns of the golden altar, which is before God; the allusion is not to the altar of burnt offering, which was covered with brass, but to the altar of incense covered with gold; and hence here, and elsewhere, it is called "the golden altar", and was a figure of the intercession of Christ; for on this altar incense was offered, which was typical of the prayers of the saints offered by Christ, through his mediation: the matter of this altar was shittim wood, a wood that is incorruptible, and of long duration, denoting the perpetuity of Christ's intercession; and its being covered with gold expresses the glory and excellency of it; its form was foursquare, as is the city of the new Jerusalem, and shows that Christ's intercession avails for all his people in the four parts of the world: and on it were "four horns", which some think represent the four evangelists, or the Gospel sent into the four parts of the world, and which is the power of God unto salvation; and for the contempt of which, in the eastern empire, the judgments signified under this trumpet came upon it; though rather these may point at the large extent and fulness of Christ's intercession, for all his people, in the four corners of the earth, as well as his power to protect and defend them, and to scatter and destroy his and their enemies.
This altar is said to be "before God", in a visionary way, as the altar of incense was before the vail, and the mercy seat, and by the ark of the testimony, Ex 30:1; suggesting that Christ continually appears in the presence of God for all the saints.
Now from hence was a "voice heard" by John, and which seems to be the voice of Christ, the advocate and intercessor.