Adopted from the book : "The Faith of Shi'a Islam" by : Allamah Muhammad Ridha al-Muzaffar"
We believe that the Imamate is one of the fundamentals of Islam (usul ad-din), and the man's faith can never be complete without belief in it. It is wrong to imitate our fathers, family or teachers in this matter, even if we respect them, for it is just as necessary rationally to consider the Imamate as it is to consider tawhid and nubuwwah. If a man does not believe in it, and supposes that it is not a fundamental of Islam, he should, nevertheless, examine the concept of the Imamate, if only to absolve himself of responsibility in this matter. The reason for this consideration is that, since we do not receive commands concerning our religious duties directly from Allah, we must refer in this matter to someone in whom we can trust, by following whom we may be sure that we will not be held responsible by Allah for having committed errors. According to our belief, the members of the Household of the Prophet fulfil such requirements.
We believe that, just as it is necessary for Allah to send someone as a prophet, so it is also necessary for Him to appoint an Imam. It is necessary that all times there should be an Imam to represent the prophet, and that he should perform the duties of the prophets, such as guiding the people, and showing them the way of goodness and prosperity in this world and the next. He ought also to hold the highest position as a public to increase among them and eliminate enmity and oppression from between them. The Imamate is therefore a continuation of the prophethood, and the reasoning which proves the former's necessity is the same as that which proves the latter's.
It is for this reason that we may say that the appointment of someone as Imam can only be accomplished by the Will of Allah through the Prophet or through the previous Imam. People cannot choose someone as an Imam because they have no authority to do so, and, should they seek to depose him: "He who dies without knowing the Imam of his time, it is as if he dies in jahiliyyah (the time of ignorance)". It will be seen from the above it is impossible for there to be a time without an Imam appointed by Allah, and that it makes no difference if human beings deny him or not, help him or not, obey him or not, or if he is absent from people's sight. Just as the prophet was absent from people in the cave and in the mountain pass, so is it possible for the Imam to be absent, It also makes no difference, logically, if the absence is long or short.
Allah has said:
And there is a guide for every people (13;7)
and
There is not a nation but a warner has passed among them. (35;24)
