It has been our learning in Madressa that every Rasul HAD to be a Nabi (Prophet) but every Nabi (Prophet) was not necessarily a Rasul (Messenger). If that learning/teaching is true then are we to understand that all Nabis (Prophets) did not have to play the role of Rasuls (Messengers)?
Answer
A rasool is a prophet who was given a new scripture. A nabi is a prophet who
had to follow the scripture of the previous prophet. Therefore, every rasool
was a nabi, but every nabi was not a rasul.
And Allah Ta’ala knows best
Mufti E. Desai