According to al-Mufid, there is an absolute necessity for prophets, since in order to know God and moral principles man needs revelation, and he noted that "every apostle (rasul) is a prophet but every prophet (nabi) is not an apostle". Although he took care to make a distinction between an apostle and a prophet as the Quran does, he did not believe that there was a difference in their functions, which enabled him to put the Imams on the level of the prophets and the apostles except in terms of their names.[6]