Muhammad (Sallallahu Alaihe Wa Alehe) was another human and would die, therefore, his exact tradition was to be followed through the line of his members of the family called " Ahlul-Bait" which is mentioned in Sura 33, Aya 33:

"And Allah only wishes to remove all abomination from you, the members of the family, and to make you pure and spotless."

The type of people must be the carrier of the tradition that are pure in their belief and in total submission to the law of Quran. Allah's desire to purify such people goes to the members of the family of the prophet. It is also commanded in Quran to follow the continuation of the tradition in your time that is called authority in Islamic laws. Sura 4, Aya 59 says:

" O you the believers, follow or obey Allah and obey his messenger and those in the authority of Islamic order."

Clearly in this matter the Islamic Authority are those who are closest to the law of Allah, the Quran and the tradition of Muhammad (S.A.W.A) as his messenger. In our life we can find the one who is the closest to his Islamic duties so he will be out Imam or leader after the death of the Prophet. This is called "Imamat."