What does Judges 5:15 mean?

Many groups sent men in response to Barak's call for fighting men (Judges 4:10). Deborah's song celebrates those communities (Judges 5:1, 14). She has mentioned willing fighters and leaders from Ephraim, Benjamin, Machir—part of the tribe of Manasseh—and Zebulun. Now she adds that "princes of Issachar" came with her. She also describes them as faithful to Barak, rushing into the valley from their mustering position on Mount Tabor at Barak's heels. The picture created is of a bold and courageous group of fighters who were ready for action.

Next, Deborah's song turns to address those tribes who did not participate in the battle. She will hold these to account for generations to come for their refusal to fight with Barak and the Lord against Israel's oppressors.

This rebuke begins with the clans of Reuben. Rather than directly refusing to come or waiting too long, they are indecisive. The tribes never move beyond thinking into action, eventually sending no men into battle. This faltering, hesitant attitude matches the description given by Jacob when he prophesied over his sons on his deathbed (Genesis 49:3–4).