‘ And Deborah said to Barak, “Up, for this is the day in which Yahweh has delivered Sisera into your hand. Is not Yahweh gone out before you?” So Barak went down from Mount Tabor, and ten eleph men after him.'
The Canaanite army were gathered at the river Kishon, not expecting an attack. After all it was they who were the hunters. The last thing they expected was for the Israelites to come down to meet them, and they would be taken totally by surprise. It was probably the last thing that the Israelites had expected either. But at Deborah's words, communicated to them by Barak, they responded. Was the Spirit of Yahweh not with her? And now she had promised that He would be with them.
“So Barak went down from Mount Tabor, and ten eleph men after him.” At Deborah's command the Israelite forces swept down the mountain - had she not promised that Yahweh had gone in front of them? - and attacked the Canaanite force, taking them by surprise.
“Is not Yahweh gone out before you?” In chapter 4 there is not a word to explain the significance of this, except as a general theological promise. Nothing is said about the rainstorm. But their victory proved it was true. Yahweh was there fighting for them. Had we not, however, had the song of Deborah we would not have had the full explanation which was that while the troops and chariots of Sisera waited by the banks of the river, heavy rains fell on the surrounding mountains causing flash floods and further heavy rains which swept down and flooded the plain (Judges 5:21), which was already possibly soggy. As a result the chariot wheels were bemired in the mud. Clad in their iron weaponry and accoutrements the footsoldiers too would find the going heavy. The song puts it in terms reminiscent of the delivery from the soldiers of Pharaoh at the Sea of Reeds.
Thus when the army of Barak, fervent and more lightly clad, and therefore more capable of dealing with the mud, suddenly and unexpectedly swept down on them they were thrown into even more confusion. Their chariots were useless, their leadership caught up in them, and the unexpected attack caught them unprepared.