What does Isaiah 13:4 mean?
In Isaiah's prophecy against the city-state of Babylon, the Lord has set aside an army to carry out His anger against the Babylonians and their rulers. This army is unique because the Lord has assembled it. Of course, those gathered do not understand they are attacking the city under God's orders (Isaiah 13:3). Their own motives are not relevant; it is God who arranges their attack, and He does so for His own purposes.Now Isaiah reveals that this army contains multitudes of fighters. They are loud, causing a great ruckus from the nearby mountains where they are staging for this battle. The army has troops from multiple nations. Many kingdoms amassed to do battle against Babylon, all of which were brought together by the Lord of Hosts.
The repeated point of these oracles is that God directs the events of human history, both in support of and against the nations of the world. They do not thrive or fall on their own. He controls everything. Israel is foolish to put their hope in powerful foreign nations instead of in the Lord.