What does Judges 5:21 mean?

How did the vastly outmatched army of Israel ever defeat the overpowering force of Sisera's Canaanite army with its 900 iron chariots (Judges 4:1–3; 14–16)? The short answer is that the Lord gave them the victory. Scripture often gives general answers without explaining exact mechanisms. In this case, the answer to "how" God enabled Israel's victory might be given in this verse: through flood and mud.

The crucial battle took place near the Kishon River, which likely was a dry riverbed the day before the battle. But Deborah's song implies an unseasonal downpour as the "stars [nature] fought…against Sisera" (Judges 5:21). The raging river is said to have swept some of the Canaanite fighters away. Others in chariots and on horses would have likely become stuck in the mud as the Kishon overflowed its banks. An army dependent on heavy chariots becomes vulnerable if the ground turns to muck and they can no longer move at speed.

This possibility is further encouraged by Deborah's command for Israel's troops to advance, leaving a position of advantage on the mountain, to attack the oncoming Canaanites (Judges 4:14). Her God-given insight into the exact moment needed to catch the floundering chariots would have turned the battle into a rout. Her command is echoed here, connected directly to the flooding of the river, giving Israel courage.