The Imam (A.S.) assured the person who inquired about these qualifications that the nation cannot be left to choose its imam without statements in this regard made by the Prophet (S.A.W.) who in turn conveys God's commandments related to this issue, for nobody other than God knows the secrets of the individuals and what they hide inside their hearts.
The Imam (A.S.) said: "Do they really realize the significance of Imamate so that they permit themselves to make a choice in its regard? Imamate is greater in prestige, more significant, higher in status, more difficult to attain, harder to achieve, than can people conceive in their minds or define according to their views, or select an Imam as they please, for Imamate became the sole prerogative of Prophet Ibrahim (A.S.), the Friend of God, second in significance only to Prophethood, whereby He honoured him, saying, `He (God) said, `I will make thee an Imam to the nations.' He pleaded: `And also (Imams) from my offspring?!' He answered: `But My Promise is not within the reach of evil-doers.'180 This verse, therefore, has nullified the imamate of any oppressor till the Day of Resurrection and became the prerogative solely of those elite persons. God, thus, honoured Ibrahim (Abraham) by allotting Imamate to those of his progeny who are the elite and who are the Purified, saying, `And We bestowed upon him Isaac and, as an additional boon, (a grandson), Jacob, and We made righteous men of everyone (of them). And We made them Imams guiding (men) by Our Command.'181 Imamate, then remained among the descendants of Ibrahim (A.S.), son inherited it from father, one century after another, till the Prophet (S.A.W.) inherited it. It was then when the Almighty God said to him, `Without doubt, among men, the nearest of kin to Abraham are those who follow him as are also this Prophet and those who believe, and God is the Protector of those who have faith.'182 Thus, Imamate became the right of the Prophet (S.A.W.) who, according to the commands of the Almighty God, and in the manner He deemed, vested it upon Ali (A.S.) and it settled among the elite of his descendants whom God gifted with the gift of knowledge and true belief."
The Imam (A.S.) continues to say: "Imamate is the status of the Prophets, the legacy of the wasis (successors of Prophets); Imamate is the caliphate of God Almighty and of His Messenger (S.A.W.)."
"The caliphate of God Almighty" has to be the prerogative of the best of people after the Prophet (S.A.W.) simply because he, the successor of the Prophet (S.A.W.), is God's caliph on earth after the demise of the Prophet (S.A.W.). His selection, therefore, has to be done by God for how can anyone judge anyone else to be eligible for it if he does not know that person's true inner self? We simply do not understand at all the wisdom of leaving the selection of the Imam to the nation without a final judgement in this regard coming from the Almighty...
source : www.rafed.net
