Verse 13. And the sixth angel sounded. See Barnes "Re 8:2-7, seq.

And I heard a voice from the four horns of the golden altar which is before God. In the language here used there is an allusion to the temple, but the scene is evidently laid in heaven. The temple in its arrangements was designed, undoubtedly, to be in important respects a symbol of heaven, and this idea constantly occurs in the Scriptures. Compare the Epistle to the Hebrews passim. The golden altar stood in the holy place, between the table of shew-bread and the golden candlestick. See Barnes on "Heb 9:1-2".

This altar, made of shittim or acacia wood, was ornamented at the four corners, and overlaid throughout with laminee of gold. Hence it was called "the golden altar," in contradistinction from the altar for sacrifice, which was made of stone. Compare See Barnes "Mt 21:12, seq. On its four corners it had projections which are called horns, (Ex 30:2-3,) which seem to have been intended mainly for ornaments. See Jahn, Arch. % 332; Josephus Ant. iii.6, 8. When it is said that this was "before God," the meaning is, that it was directly before or in front of the symbol of the Divine presence in the most holy place. This image, in the vision of John, is transformed to heaven. The voice seemed to come from the very presence of the Deity; from the place where offerings are made to God.