What does Revelation 9:13 mean?

According to this verse, the sixth angel blows his trumpet, and the apostle John hears a voice from the four horns of the golden altar before God. As described in Exodus, the altar in the temple had four curved projections on the corners (Exodus 27:2). The sixth trumpet judgment involves this voice speaking, giving orders to angels who unleash a massive army, causing the death of one third of earth's remaining population.

Contrary to the opinion of some doubters, God is not a disinterested Creator who winds up the world like a watch and then retreats to let it run down on its own. He is very much involved in what happens on earth. This verse shows He is involved in what takes place under each trumpet judgment. When the sixth angel blows his trumpet, heaven responds. Although an invasion from the northeast is about to begin, God is behind the scenes. He uses the invasion to chastise apostate Israel. It should encourage believers to know God understands and is in control of what happens on earth. He sees even the sparrow's fall and has numbered the hairs of our head (Matthew 10:29–30). Nothing can separate a believer from God's love (Romans 8:35–39).