The ahl al-Bayt and The Legacy of Prophet hood.

As-Salaam alaikum,
In the Holy Qur'an, Allah Ta'ala says :--

"Allah only wishes to remove all abomination from you, O members of the household (family), and make you pure and spotless." (33:33)

And in the Hadith, we have it where the ahl al-bayt are defined and accorded significant role in the development of the Muslim Community. An important narration we have on the Members of the family of the Prophet, Sallallahu alaihi Wasallam, the ahl al-bayt, is the Hadith al-Thaqalayn or the narration of the Two Weighty things. The Hadith is the one where the Prophet, Sallallahu alaihi Wasallam, said :--
"I am going to leave with you 2 heavy burdens. The first of them is the Book of Allah : in it is the true guidance and the light. Therefore, hold fast to it, and my household. I remind you of Allah in matters relating to my household. I remind of Allah in matters relating to my household. I remind you of Allah in matters relating to my household. "(Sahih Muslim, Musnad Ahmad).
Who are the ahlal-bayt?
The family of Prophet Muhammad, Sallallahu alaihi Wasallam, or the ahl al-bayt, are referred to in the Hadith as the ahl - kisa', that is the people of the cloak. The hadith gives an account of an incident whereby the Prophet, Sallallahu alaihi Wasallam, gathered 5 members of his family, that is Ali, Fatimah, Hassan and Husayn, may Allah be pleased with them, under his cloak. According to the tradition, it was at this time that the ayat quoted above... the ayat al-tahir (33:33) was revealed.
A narration attributed to A'isha, may Allah be pleased with her, found in Sahih Muslim, reads :--
"Allah's Apostle, Sallallahu alaihi Wasallam, went out one morning wearing a stripped cloak of the black camel's hair. Then came Hassan Ibn Ali. He wrapped him under it, then came Husain and he wrapped him under it along with the other one (Hassan). Then came Fatimah and he took her under it, then came Ali and he also took him under it and then recited : Allah only wishes to remove all unvleanliness from you, O people /members of the household, and purify you, a thorough purification. "
(Muslim, Book 31, No. 5955)

The descendents of the above mentioned ahl al-bayt members will continue as inheritors of the Prophetic message in Islam, and will embody and spread the message of the Prophet, Sallallahu alaihi Wasallam, to the end of time on earth.
Today, as it has always been since the Prophet left this world, the function of the family of the Holy Prophet, Sallallahu alaihi Wasallam, is the perpetuation of the practices of the Sunnah of the Prophet, Sallallahu alaihi Wasallam. In this regards, you will see/note that the great Awliya or Saints of Islam were the Spiritual Poles (aqtab) for the Muslim community in general and for Sufi Orders as well... and most of them, if not all, came from the progeny of 2 of the ahl al-bayt, that is Hassan and Husayn, may Allah be pleased with them.
The ahl al-bayt are bound up with the function of Prophet hood. Specifically, their role is to preserve the dissemination of Qur'anic decrees and the truths of Islam. The family of the Prophet, Sallallahu alaihi Wasallam, the ahl al-bayt, are the repositories and examples of the Holy Prophet's Sunnah. In the Hadith al-thaqalayn, the second of the 2 weighty things that the Prophet said he left behind is/are the ahl al-bayt. In another ahadith, as noted in Bediuzzaman's work, it was his Sunnah or Practices that were the second thing he left behind. Therefore, what the Prophet, Sallallahu alaihi Wasallam, meant by "weightness" of his family was their embodiment of his Sunnah.
In his 'Flashes Collections and Letters', published between 1928-1932, Sa'id Nursi observed that the love and compassion that the Prophet, Sallallahu alaihi Wasallam, had for Hassan and Husayn was not only due to the familial bonds between them but also because "they were each the tip of a luminous thread of the function of Prophet hood, and the source, sample and index of a community of great consequence which would receive the legacy of Prophethood."
In other words, through the ahl al-bayt the legacy of Prophethood was /is passed from generations to generation, they illuminate the way of the Holy Prophet, Sallallahu alaihi Wasallam. The ahl al-bayt have been, and are, exemplars of the way of Prophet Muhammad, Sallallahu alaihi Wasallam, embodying the standards of excellence for spiritual struggle and progress.