The Rambam makes a point of showing a proof why the prophecy and leadership of Moshe Rabbeinu was ordained directly by Hashem. We are not to believe in the validity of Moshe's leadership based on the miracles he performed.
The Rambam was concerned that in time people would find reasons in nature as to how to explain supernatural events.
The key Pasuk is where Hashem tells Moshe that He will appear to Moshe in the thickness of the cloud בעבור ישמע העם בדברי עמך וגם בל יאמינו לעולם, in order that the people hear when Moshe was being spoken to by Hashem and in order that they believe in you forever.
Never in the history of mankind, did a few million people hear G-d empowering a leader, Moshe, to direct עם ישראל. This is why we believe in Moshe Rabbeinu.