Yeshayahu Leibowitz commented on the last verse of this parasha, with reference to Rashi’s commentary. The verse states that “he heard the voice communicating with him…”.The masorah gives the vocalisation of the word as “middaber” rather than the usual “medaber”. This is in the reflexive form indicating an action reflecting back to the individual who performs it. Rashi stated that “middaber” is like “mitdaber” indicating that G-d was speaking to Himself and Moshe heard from his inner self. Leibowitz explained that this was not an acoustic event in which the sound reached Moshe.
Rather, there was a process in the self-awareness of Moshe whereby he heard G-d speaking to Himself. He understood G-d’s meaning, hearing G-d’s voice from within his own self. Rashi anticipated the view of the Rambam who wrote that prophecy was something which occurred in the self-awareness of the man who had reached the ultimate degree given to man in perceiving G-d. Leibowitz argued that because Rashi and Rambam expressed the same view, this must indicate a feature of basic faith. It was a point not previously noted by any of the previous commentators, but then, 400 years after Rashi, developed by R’ Ovadya Seforno. He taught that G-d does everything for Himself and by knowing Himself, He knows and does good to others and the action manifests itself to the one affected by G-d in accordance with his capability.
Rashi thus explained that where it states in the Torah “ and G-d spoke”, the listener heard according to his capability, indicating a way of understanding the meaning of G-d’s speaking to man.If Aaron had been there he would not have heard anything.