The Lord has declared...
The Lord has declared: "Verily We sent down the Reminder (The Qur'an) and Verily, We (Ourselves) shall be its Guardian." Holy Qur'an 15:9 To preserve the Holy Qur'an in its original purity both in its verbal form as well as its meaning, and to keep the divine guidance always current and ever available to every seeker after truth, the Holy was not sent alone into the world.
As Aaron was given to Moses to assist him and to succeed him, along with the Holy Prophet, his cousin Mi, son of Abu-Taleb, from the same holy family of Abraham, was given his advent, to be his Vicegerent and his Successor.
Thus was started the line of the Holy Imams (i.e., the Divinely Commissioned Guides) who were destined to be the authentic custodians of the Holy Qur'an, and as the fountainheads of the correct knowledge of the Word of God, to guide mankind towards the correct belief and the proper practice of the Faith. If these guides, the Holy Imams, had been from any family, other than the family of Muhammad, it would have been mis- construed as another authority parallel to that of the Holy Prophet.
The grace of the Lord, avoided this confusion and established one single authority of the Last of His apostles, as the unique one, with the unity of purpose. Hence it was divinely destined that the line of the Divine Guides called the Jmams, to succeed the Last Apostle, also, to be from the same stock of the Holy Family of Abraham, and this was also the covenant with Abraham.
" And as for Iskmael, I have heard thee ; Behold, I have blessed him and will make him fruitful and I will multi- ply him exceedingly, TWELVE PRINCES shall he beget and I will make him a great nation. Gen. 18 :20 Both the Holy and his Vicegerent Ali were brought into the world from one and the same family, with whom the Lord had established an Everlasting Covenant (Gen. 17 :7, 8).
Muhammad to be the Promised Last Apostle, the 'Comforter' the ' Spirit of Truth' the ' Holy Ghost', and the 'Maetrea' prophesied by Buddha, and Ali his cousin, his adopted son, his son-in-law and his Vicegerent to be the starter of the line of the Promised Twelve Princes or the Twelve Holy Imams in the seed of Abraham, through Ishmael.