Abstract:
It is necessary for people to have a leader and a guide who draws them nearer to righteousness and abandoning corruption. Having such a leader is a blessing and grace of God. In Shi‘i Islam, the concept of Imamate is the necessity of having a leader who is appointed by God and
will lead the ummah after the Prophet’s death. The Imam surpasses the people in all admirable qualities such as piety, knowledge, courage, and wisdom. He must also be infallible (ma’soum) as this trait ensures that he is trusted, obeyed, and is capable of defending divine law. Thus, the Imam carries the role of both continuing the task of the Prophet in presenting true Islam as well as being a political leader. An Imam is appointed only by God; the Prophet merely
announces an Imam’s infallibility to the people. On the other hand, the Sunnis in theory believe that it is the responsibility of the people to appoint a caliph. In what follows, we will
refer to the appointments of the Imams by God and the particular case of who was appointed after the Prophet’s death.
Machine summary:
"The Prophet then said, ‘Gabriel has brought me a command from my Lord to stop here and announce to all people, whether black or white, that Ali, the son of Abu Talib, is my son, my wasiy, my successor, and my caliph and Imam after me.
This verse was revealed when the Prophet gathered the people on the Day of Ghadir and asked them to believe in the Imamate of Ali and pay allegiance to him.
Because it was only after Imamate was declared publicly that Allah said, "Today the faithless have despaired of your religion…" Even though the Prophet mentioned many cases of Imam Ali’s successorship before the Day of Ghadir, the people realized that the significance of this event verified his leadership.
When the Prophet asked the people to pledge allegiance, and God said, "Today I have perfected your religion for you, and I have completed My blessing upon you, and I have approved Islam as your religion," he implied that all the details of Islam had been explained while only one final aspect was missing, rendering Islam imperfect until the revealing of this verse.
If we do so, we have recompensed the Prophet, which only serves as our benefit as it is the straight path towards God. As to why the verses of the Qur’an do not explicitly reveal Imam Ali’s successorship is perhaps because of the threat that if the Imam’s appointment was clearly announced, it would have been distorted by those who rejected him (a), just as hadiths were banned from being written after the Prophet’s death for the same reason."