What is the Pasuk telling us here?
Rashi #1 (by implication) and Seforno: When Hashem instructed Moshe to speak to Pharaoh, 1 Moshe complained that Pharaoh would not listen to him, 2 at which point Hashem instructed Aharon to accompany Moshe. 3 It was not Hashem's intention that Moshe and Aharon should act in the same capacity, but rather that Moshe should be Pharaoh's 'god,' and Aharon, Moshe's interpreter. 4
Rashi #2 (to 12:2): It is teaching us that Hashem only spoke to Moshe in daytime. 5
Ramban: With reference to the previous Pesukim, 6 the Torah is informing us that, although Moshe and Aharon were both responsible to take Yisrael out of Egypt, Hashem issued the instructions to Moshe exclusively. 7
Targum Yonasan: Since Hashem spoke to Moshe exclusively, it emerges that Aharon, who was equally obligated to speak to the people, 8 listened carefully to everything that Hashem commanded Moshe.
6:29.
6:30.
6:13.
See 7:1. Gur Aryeh - Rashi must connect our verse, 'It was on the day that Hashem spoke...', to the following verses; because otherwise, the information is missing from our Pasuk. What took place that day?
As opposed to all other prophets, to whom Hashem spoke in a vision by night. See Keli Yakar.
As opposed to Rashi and Seforno, who explain that it pertains to the Pesukim that follow. See Sifsei Chachamim.
See Parshas Bo, Shemos 12:2 - Perush Yonasan, based on the Mechilta.