If Mishneh Torah also comes from Hashem, how is it different from the first four sefarim?
Mishneh Torah was not Moshe’s own words; it is the word of Hashem, as it became united with Moshe’s intellect.
Moshe said Mishneh Torah with ruach hakodesh. A similar thing can be said about the tzaddikim and chachmei Yisroel of each generation.