Differences between Nabi and Rasool

by Mount Sinai

Nabi is the one who knows the message of Allah. Rasool is the one who conveys the message of Allah. Before conveying the message one has to know the message first. In that sense, a rasool is also a Nabi in the first place.
There is no logic for such command to obey Nabi. A Nabi (who is a human being) can convey anything. When a Nabi conveys message of Allah then he becomes (or performing as) Rasool of Allah. ‘Obey Rasool’ actually means to obey what is conveyed (the message of Allah). It doesn’t mean to obey whatever a human being says or commands.