Imam Ar-Ridha’ (a.s.) said:
اَلإِمامُ أَمينُ اللّهِ فِى أَرْضِهِ وَ خَلْقِهِ وَ حُجَّتُهُ عَلَى عِبادِهِ وَ خَلِيفَتُهُ فى بِلادِهِ وَ الدّاعِى اِلَى اللّهِ وَ الذابُّ عَنْ حَرِيمِ اللّهِ.
The Imam is the trustee of God on earth and among His people, and His proof for the servants and His representative in the cities and summoner towards Him and protector of divine sanctuaries.1
In this tradition, which is part of a detailed tradition on the concept of Imamate, reference is made to five aspects of the heavy and important duties of an Imam :
1- Imam is a treasurer and trustee of revelation and protector of all sciences, commands and knowledge of religion.
2- Imam is a living proof of divine religion.
3- Imam is a divinely appointed supervisor and authority and God’s representative among people.
4- Imam is the one who calls people towards goodness and forbids evil and is the greatest emissary of religion.
5- Imam is a protector of divine sanctuaries against the invasion of enemies .
To carry out such tasks requires someone who has access to divine knowledge and is infallible. True Imams are the ones with these qualities and nobody except God can appoint them.