On the eigth and last day of Miluim, the dedication of the Mishkan, at the height of Simcha and Kedusha, suddenly two sons of Aharon are killed, and Aharon stands silent.
Why is Aharon silent? How can HaShem do this to him, Davka on this day of perfection?
The name Miluim hints at the answer. Something had to be filled, completed, during the days of Miluim. That something is related to what happened at a previous "Simcha," the one around the Golden Calf. Chur dared to confront the idol worshippers and was murdered by them. Subsequently, Aharon cooperated.
In the face of Chilul HaShem, a Jew must be prepared to fully trust HaShem, and sacrifice himself, if need be. Certainly the Kohen Gadol must act this way. Aharon failed, and this was his sin.
The days of Miluim come to repair. Therefore, at the completion of the days of Miluim, something had to happen that could make up for the sin. Aharon has to accept the death of his sons, who died in a sense in his stead. He understands, and stands silent. His acceptance is the repair.
[After Rabbi Meir Kahane, Or HaRayon, Chapter 17 (Mesirut Nefesh)]
