Rashi and Rashbam: In fact, this is synonymous with Hashem's command in 6:11. ¹

Ramban (to 6:13) ² : Moshe now assumed that, from now on, he together with Aharon would prophesy and would perform all the miracles before Yisrael and before Pharaoh, and that Aharon would be the spokesman. But Hashem said to him, "Ani Hashem" - reminding Moshe that it was to him alone that Hashem revealed His Great Name, and that he alone was the Shali'ach who would issue Pharaoh with instructions. ³

Oznayim la'Torah #1: Having in mind Moshe's Eimas Malchus - particularly bearing in mind that he was worried about his speech defect, Hashem was warning Moshe to say to Pharaoh everything that He had told him, word for word.

Oznayim la'Torah #2 (citing Ma'aseh Hashem): Hashem was incorporating even things that were merely intended to harden Pharaoh's heart, in order to increase His signs and wonders in Egypt.

Oznayim la'Torah #3: Whereas on the previous two occasions that Hashem had spoken with Moshe - on Har ha'Elokim and in Midyan, He had only instructed him to speak to Pharaoh once; ¹ now He was ordering him to speak to him on an ongoing basis - virtually prior to each of the ten plagues.