Rashi is known mostly for being concise, but one of his other notable characteristics is his humility.
When Moshe ascends Har sinai to get the Torah he leaves Aharon and Hur in charge of the people at the foot of the mountain. Meanwhile, his faithful servant, Yehoshua, follows Moshe up the mountain.
In answer to the question for what purpose did Yehoshua follow Moshe up the mountain, Rashi says, “I don’t know.”
To understand the question we need to understand where Yehoshua was during the giving of the Torah. More accurately, we need to understand where he wasn’t.
We know that he was not with Moshe on top of the mountain while Moshe was receiving the Torah.
But we also know that he wasn’t with the people, because later in the Torah Moshe meets Yehoshua on his way down from the mountain and Yehoshua was unaware that the people had built the golden calf or of any of the activities surrounding it.
Rashi surmises that Yehoshua followed Moshe half way up the mountain. Far enough away from the people so he didn’t know what was going on down there, and far away enough from Moshe so he didn’t know what was going on up there. He remained the whole 40 days and 40 nights in a no-man’s land, half way up the mountain.
Rashi suggests that Yehoshua may have done so in order to show respect for his teacher Moshe by escorting Moshe as far as Yehoshua was allowed to go. And then he just waited for Moshe to come back.
I suggest that this Rashi is not a display of humility, rather Rashi is giving a veiled critique of Yehoshua’s leadership.
Rashi is not saying, “I don’t know what Yeshoshua was doing there.” Rather he is saying, “what the heck was Yehoshua doing there???”
We have only encountered Yehoshua once before. He was the strong military leader who heroically galvanized the people against their most vicious enemy Amalek, and lead them to victory. We don’t know much about him, but he must have been charismatic and capable, and we can be sure that he had earned the respect of the people.
Aharon and Hur, whom Moshe had left in charge were not capable of stopping the people from building the golden calf. But what if Yehoshua had been there? Is it possible that he could have prevented one of the greatest sins and most tragic moments in Jewish history?
Yehoshua abandoned his post with the people, a major responsibility, in order to escort his teacher Moshe, a very minor responsibility. This showed a lack of judgement, and bad leadership.
A common pitfall for leaders is sometimes focusing on a minor accessible problem as a means of rationalizing avoiding a larger and more difficult problem. Part of leadership is recognizing which responsibilities are immediate, and which can wait until later, be done by someone else, or can be neglected entirely.