Al-Sheikh Al-Mufid reported that Al-Mamun Al-Abbasid told Imam al-Rida (a.s), "Tell me the greatest merit of Ali (a.s) mentioned in Qur'an."
Imam al-Rida (a.s) said, "his merit in Mubahala", Then, Imam (a.s) recited the al-Mubahala verse and said: "The Prophet (p.b.u.h & his family) called Al-Hassan (a.s) and Al-Hussain (a.s) who were his sons and Lady Fatima (a.s) who is the reference for "women" in this verse and Imam Ali (a.s) who is the "soul" of the Prophet (p.b.u.h & his family) in the word of God. And it is known that no one in creation is higher than the Prophet (p.b.u.h & his family), then according to the word of God, no one should ever be higher than the soul of the Prophet (p.b.u.h & his family)." (3)
Imam Ali (a.s) being the self of the Prophet in the true sense is not possible, hence what is intended in the verse is the figurative meaning. The closest metaphor to the true meaning in this situation is that he (a.s) is equal to the Prophet in all particularities, except for what was brought out by the evidence, which is prophethood. Since there is no prophet after Muhammad (p.b.u.h & his family).
One of the peculiarities of the Messenger of God is that he is the best and greatest of Allah’s creation. Acknowledging the foolishness of the preference of the ignorant over the virtuous, it is necessary to prioritized Imam Ali (a.s) over others in being the caliph of Muslims and the Islamic Umma.
(1) Al-Quran, 3:61.
(2) History of Damascus, v.42, p.431-433
(3) Al-Mufid’s Works, v.2, p.38.