The Duties of the Imam
The characteristics and duties of the Imam are as follows.
1. He knows all sciences, teachings, commandment, and rules of the religion, not from revelation, but through the Prophet’s (s) training and other sources that will be mentioned later.
2. He tries to propagate Islamic teachings and commandments and fight religious deviations.
3. He enforces political, social, judiciary, legal, punitive, and economic rules of Islam; that is he continues the Prophet’s (s) Islamic government based on Islamic criteria.
4. The Imam, like the Prophet (s), is completely away from mistakes, forgetfulness, and intentional wrongdoing. He is, in fact, infallible; otherwise, Allah’s purpose of guiding humans and introducing the true path toward perfection would remain incomplete and His Mercy would not be accomplished.
The Shiah argue for human need to the Imam, his knowledge and infallibility, and the necessity of his appointment by the Almighty Allah based on the famous Mercy (lutf) principle, considering the existence and appointment of the Imam as a sign of Allah’s Mercy.
The late Allamah Hilli writes, “The existence of Imam is because of Allah’s Mercy and appointing the Imam is obligatory upon the Exalted Allah, so that His purpose is accomplished!”
The Imamiyyah (Shiah) Muslims know the Imam a noble person, who is the best one in his age in regard to belief, commitment to ethical virtues, true knowledge of Islamic commandments and rules, and devoutness, after the Messenger of Allah (s). He is infallible and away from mistakes, forgetfulness, wrongdoing, and sins. Only such a person can be the Prophet’s (s) successor and the people’s leader.
The Sunni Muslims, however, do not necessitate these conditions for the successor of Prophet Muhammad (s). They even do not nullify the probability of mistakes or wrongdoing for him. They think that qualification for ruling and managing worldly issues suffices for the Imam. The Sunni Muslims consider obeying the Imam obligatory for the people and opposing him forbidden.
 Sharhi Tajrid, p. 284.