Settling The Score

When Moshe asked the Jews to go fight the Midianites, they refused. They needed to be impressed into service. Why? Because they knew that Moshe was to die after this war, and were demonstrating how much Moshe meant to them. (Rashi)

Who had told them, and why?

It would seem that Moshe himself told them. In fact he was instructed to speak about it to the Jewish people. Why did the Jews need to know?

The battle being waged was a personal satisfaction for Moshe. The Midianites had deeply hurt the Jews, and the debt, the score to settle, was still unpaid. The Jews were now to make the Midianites account for their deeds, and settle with them. Hashem did not want Moshe to die without seeing the revenge visited on his foes, without being vindicated. And He promised “take revenge from the Midianites and (only) then die”

And the Jews were entitled to learn that Hashem was holding off Moshe’s death so that he could have the satisfaction of seeing revenge. They were to learn that even in resolving insult to ones person, Hashem takes care of tzaddikim.