What was Yehoshua doing on Har Sinai?
Rashi: Yehoshua accompanied his Rebbe, Moshe, as far as the border of the mountain, 1 where he pitched his tent and awaited Moshe's return. 2
Ramban: He was one of the seventy elders who accompanied Moshe part of the way out of the camp. 3 Now that Moshe left them to ascend the mountain, Yehoshua accompanied him up to the border.
Since that was as far as he was allowed to go (Rashi).
And we see from the Pasuk in Ki Sisa, Sh'mos 32:17 that he was not with the people when Moshe returned (Rashi).
Ramban: Nevertheless, he was not punished together with the elders in Tav'eirah (Refer to 24:11:3:1*), because he was worthy of Divine visions and all prophecy (Refer to 24:11:2:3).
Why does the Torah inform us three times that Moshe ascended the mountain?
Oznayim la'Torah: It is comparable to the three levels 1 of Kedushah of the Mishkan - the Azarah, the Heichal and the Kodesh Kodshim. Here too, first Moshe ascended the section of mountain that had the Kedushah of the Azarah, then the section that had the Kedushah of the Heichal, and finally, after separating and preparing for six days, he ascended the part of the mountain that had adopted the Kedushah of the Kodesh Kodshim.
Mi'd'Oraysa - See Oznayim la'Torah.
