Here we come to the question about the necessity of Imams as Shiites believe, although there is Koran and Sunnah (i.e. his rituals and teachings). There are many reasons expressed to justify the necessity of Imams, but we refer to the simplest one, which explains that when there is a need for the prophets there should be a need for Imams as well. Since Islam is the final religion and Mohammad the last prophet, it should be able to accomplish all human beings needs up to the end of the world. On the other hand, while fundamentals and the general concepts of Islam are expressed in Koran, the clarification and elaboration is a burden for the prophet to be carried. And it is clear that the prophet, as the leader of the community, interpreted Koran according to the necessities of his era. Therefore, his successors should be competent and linked to the divine source of Koran in order to clarify whatever the prophet had not elaborated so and fulfill the people's needs during the passage of time. Imams, the guardians of the heritage the prophet left behind and the real interpreters of Koran saved Islam from the malevolent and biased foes, keeping this source eternally pure. Notwithstanding, Imam as a transcendental human is a complete and unadulterated model in any aspect of humanity to be followed, upon whom man is definitely reliant to be inculcated due to his assistance and guidance and remain safeguarded from deviations, carnal traps of the self and outside devils. All this stresses the importance and necessity of Imams being the leaders with the following responsibilities: 1. To lead and manage the society (to establish a government) 2. To safeguard Islam from deviations and convey true interpretation of Koran 3. To refine and purify the selves of people and guide them toward salvation