As the Torah unfolds Moshe shows his humanity in frustration and anger. In parshat Matos, Moshe tells the people to fight and kill Midianites. The warriors of israel spare the women and spoils of war.Moshe gets
Angry. When it comes time to teach Israel about ritual lawis out the weapons of war, it falls to eliezer to teach.
Rashi says that his equilibrium or ability to teach the lae clearly is muddled. He cites other places where Moshe is angry and cannot fulfill his mission as a teacher.
The shikkerdovid has a personal stake in this lesson. The shikkerdovid is often wont to emotion or anger. Therefore, this lesson really hits home. Our mission in life is obscured or denied us if we allow anger to overcome.