The Imam is a spiritual leader in Shia Islam. He is not a clergyman, as a Catholic priest would be, but is rather Allah's chosen representative. They are believed to be the ultimate example of faith in Allah. One branch, the "Twelver Shia" believe that there are twelve Imams, who are considered to be infallible, incapable of committing any sin. They are the rightful successors of Muhammad, and Allah's chosen representative to protect both Islam and the Qu'ran. They are chosen by Allah to be examples of the faithful life. So important are they to Shia Islam that only Allah may choose them; they cannot be chosen by ordinary Muslims. Shia Muslims believe that Ali, Muhammad's successor was the first of the Twelve infallible imams, chosen by the Prophet himself, as indicated by the following remarks by Muhammad:
Oh people! Reflect on the Quran and comprehend its verses. Look into its clear verses and do not follow its ambiguous parts, for by Allah, none shall be able to explain to you its warnings and its mysteries, nor shall anyone clarify its interpretation, other than the one that I have grasped his hand, brought up beside myself, [and lifted his arm,] the one about whom I inform you that whomever I am his master, this Ali is his master; and he is Ali Ibn Abi Talib, my brother, the executor of my will, whose appointment as your guardian and leader has been sent down to me from Allah, the mighty and the majestic.
In contrast, the Imam for Sunni Muslims is the appointed leader of a congregation, and normally delivers the Friday sermon, although he is not considered a clergyman.