The Prophet’s Positions
It is proved in kalam books that Prophet of Islam (s) had several positions during his lifetime:
1. Having relation with the invisible world and getting revelation from the Almighty Allah,
2. Maintaining religious knowledge, teachings, commandments, and laws descended as revelation,
3. Propagating this heavenly collection among the people, answering their questions, and fighting superstition,
4. Enforcing political, social, judiciary, economic, legal, and punitive Islamic commandments, defending Islam and the Muslims, and establishing Islamic government.
Prophet Muhammad (s) was always away from mistakes and forgetfulness in fulfilling these duties. He was also infallible and away from committing sins and crimes. If a prophet is not infallible, religious commandments and rules are not guaranteed and Divine Mercy is not accomplished.
This is, in fact, the Shiah viewpoint, who believe that just as human being needs Divine knowledge, teachings, and rules revealed to prophets (`a) for reaching material and spiritual perfection, he needs to have an infallible leader who undertakes the Prophet’s (`a) responsibilities and follow his goals in the absence of the Prophet (s) throughout history. Otherwise, the prophets’ (s) mission in guiding human beings will remain incomplete. Human need for religious sciences and teachings is not limited to the Prophet’s (s) age; humans need this Divine Source of knowledge in all ages. The short time of Prophet Muhammad’s (s) prophetic mission did not secure this continual need; especially because of termination of prophetic missions ever.
The Shiah Muslims know the Imam as a brilliant complete human, who succeeds the Prophet of Islam (s) and undertakes all his duties, except receiving revelation.
 Speculative theology.