What was the grievance? – Mattot
In Numbers 31:1, God tells Moses to “Avenge the Israelites on the Midianites”.
What was the grievance which Israel had against Midian?
The Midianites had tried to entice the Israelites away from their adherence to God.
But isn’t it strange that amongst the desert tribes that opposed Israel, the Midianites but not the Moabites were treated so harshly? Weren’t the Moabites also guilty, also deserving of punishment?
Rashi gives a psychological explanation. He says that the Moabites were not in themselves God-deniers. They were believers in God but were frightened of the numbers and strength of the Israelites. They thought that if they cursed the Israelites with sufficient power it would reduce the threat.
On the other hand the Midianites thought it would work if they succeeded in getting Israel to abandon God.
Both tribes were against Israel; Midian was also against God.