The greatness of the Prophet’s (s) Ahlul-Bait, the five people of the cloak – namely Prophet Muhammad (s), Hazrat ‘Alī, Fātimah, Hassan, and Hussayn (a), have been mentioned in many traditions related by Shia and Sunni narrators alike. The reason that the Prophet (s) emphasized these people’s positions was not because of family relations, rather because of their merits which stemmed from their high level of thinking, actions, goals, and ideals that they hold dear. They did not think about anything other than Allah and gaining his satisfaction and were always important factors in protecting Islam, explaining religious rulings, and guiding mankind towards perfection. For them to carry out these responsibilities it was necessary to make these emphases in their favor in the best way possible.
Ahlul-Bait, as a Quranic, traditional, and theological term means the Prophet’s family (s). This term has been used to mean this in the verse of purity (33:33): “Verily, Allah desires to rid you of all impurities, Ahlul-Bait, and purify you a thorough purification.”
Commentators of the Quran say regarding this verse that what is meant by Allah’s desire is a natural desire because Allah’s legislative desire has been coupled with the purity of all humans. Everyone is able to reach purity from sin by obeying the teachings and rulings of Allah, the wise. But, Allah’s natural desire for purity is exclusive to the Ahlul-Bait of the Prophet (s). This means that there is no sin or mistakes found in this family and this would not be the case except if they had an important role to play in executing the goals of Islam.
The philosophy behind the Quranic and traditional emphasis in proclaiming the Ahlul-Bait’s high position was: their high level of thinking action, goals, and ideals that they hold dear. They did not think about anything other than Allah and gaining his satisfaction. The Quran gave an example of the Ahlul-Bait’s selflessness in Sūrah Dahr: “Give your food that you like to the needy, orphan, and captive (and say): ‘I feed you because of Allah and I do not want anything in return from you.’”
The biographies of the Ahlul-Bait (a) and their teachings are the best pieces of evidence that their goals where nothing except to raise the words of the oneness of Allah and to negate all forms of polytheism and deviance.
They were always important factors in protecting Islam, explaining religious rulings, and guiding mankind towards perfection. This special importance that they gave to religion and Islamic rulings caused their emphasis so that people will understand that they have high positions and take their guidance in reaching to perfection. The main purpose of the Quran is guidance: Alif-lām-mīm; this book has no doubt in it; a guide for the pious. Whoever pays a little attention to the verses of the Quran can easily accept this deduction. Since the Shia Imāms were the guides of the nation they were called the Ahlul-Bait. Because of this the Prophet (s), who is the real commentator of the Quran, when he wanted to mention the position of religious leadership after him, used the term Ahlul-Bait, for example when he said:
“I am leaving amongst you two momentous things; one of them is the book of Allah and the other my Ahlul-Bait. If you cling to these two things you will never go astray. They will never become separated from each other until they enter the Fountain of Kawthar in the hereafter.”
Or: “My Ahlul-Bait is similar to Noah’s ark: whoever got on it was saved and whoever refrained from getting on it was drowned.” According to this the role of the Ahlul-Bait (a) in protecting the religion, explaining the rules of the religion, caring for the people, and guiding the society is so important that separating oneself from them is equal to drowning or destruction. They do not have any goal other than inviting to Allah’s path.
 «انما یرید الله لیذهب عنکم الرجس اهل البیت و یطهرکم تطهیرا»
 Al-Mīzān (Farsi edition), v.16, p.467
 Sūrah Insān: 8-9 « وَ یُطْعِمُونَ الطَّعَامَ عَلىَ حُبِّهِ مِسْکِینًا وَ یَتِیمًا وَ أَسِیرًا،إِنمََّا نُطْعِمُکمُْ لِوَجْهِ اللَّهِ لَا نُرِیدُ مِنکمُْ جَزَاءً وَ لَا شُکُورًا».
 Sahīh Tirmidhī, v.2, p.380; Ahmad bin Hanbal, Musnad, v.3, p.17: «انی تارک فیکم الثقلین کتاب الله و عترتی اهل بیتی ما ان تمسکتم بهما لن تضلوا بعدی ابداً فانهما لن یفترقا حتی یردا علیّ الحوض»
 Hākim, Mustadrak al-Sahīhayn, v.2, p.432; Fīrūzābādī, Fadā’il al-Khamsah, v.2, p.65: «انما مثل اهل بیتی فیکم کسفینة نوح من رکبها نجا و من تخلف عنها غرق».
 For more information refer to: The Ahlul-Bait and verse 23 of chapter Shura (question 160), the reason that the Ahlul-Bait is limited to a few people (question 243), and the Prophet’s (s) Ahlul-Bait (question 833).