It is necessary to pay attention to the following points:
(1) The sound mind of any human being accepts that knowledge of the past and present, and its utilization is absolutely necessary. By innate nature, he relies on a series of news and information concerning rules and ethical issues. A minute observation reveals that man’s individual and social life is indebted to the collection of information on various subjects where he has personally neither investigated nor experienced all by himself. Basically, it is not possible for any individual to investigate and experience all the aspects. Rather, by relying on the information of the past and present, he arranges his ordinary and scholarly life and avails himself of its results.
Without reliance on information, can anyone gain certainty about the past sciences, historical events and happenings, existence of personalities, cities and places?
Who can witness by himself the smallest as well as the most important of information and news of the past? Has every individual experience(s) the formula for all the various sciences? How has man succeeded in benefiting from the past sciences? Was it from individual experience? Who recognizes the parents of children out of experimental and scientific reasoning? In the entire human societies, how many have witnessed birth and delivery of children so that they acquire certainty that so and so are their parents!?
All these are possible, only and only, through narration by reliable persons. Most of the phenomena of human life, and civil and religious laws, are the outcome of experimental information, all acquired through narrations.
(2) Islam is a religion based on divinely granted consciousness (Fitrat). While it is the basis of acquiring the principles of human Fitrat, it also calls the people to keep this Fitrat awake. Its lucid principles and doubtless precepts call us to rely on the sayings of the prophets and Imams that were famous as trust and confidence during their respective lives.
During the length of history, the believers and others who weren’t stubborn, relied on Noah, Abraham, Moses and Jesus, and believed Muhammad as a prophet who from his youth was famous as“Muhammad-e-Amin” . They reckoned his sayings to be revelation and accepted and acted upon his warnings regarding the Day of Judgment and chastisement!
(3) The same innate path exists for acquiring Islam and whatever has been taught by the holy Prophet (s.a.w.a.). For a research and study about Islam, there exists no way save the Qur’an and traditions; although these sayings are pondered over and appreciated by the mind.
The basis and foundation of the lofty structure of religion is formed by innate rational mind. In this regard, the holy Qur’an (the first source for the Muslims for acquiring the concepts of religion) has confirmed this innate path and leads its readers towards it. In various verses, the holy Qur’an has given validity and authority to the holy Prophet’s sayings, deeds, and advises so that the Muslims follow him. For example verse 7 from chapter Hashr says:
“Whatever the Apostle gives you, accept it, and from whatever he forbids you, keep back.” (Qur’an, 59:7)
It’s clear that aside from commands and prohibitions, the holy Qur’an sets forth other matters too; and intends to strengthen the Prophet’s position. Undoubtedly, these sayings and deeds too amount to Divine command and alongside the Qur’an, they form the total set of religious teachings and realties.
“Obey Allah, and obey the Messenger, and those in authority from among you.”
It is cleat that obedience to the holy Prophet (s.a.w.a.) and those vested with authority, is different from obedience to Allah’s commands (as the word ‘obey’ is repeated). Although the words of the holy Prophet (s.a.w.a.) and Imams (a.s.) are only based on revelation and just as mentioned before, the aim for obeying them is only to strengthen their position, nevertheless, the wordings and interpretation of the verse opens the door for acting upon the Hadith and sayings of the Prophet (s.a.w.a.) and Imams (a.s.).
It’s necessary to remind that while the holy Qur’an is guidance and light; by Divine Wisdom, the holy Prophet (s.a.w.a.) and his true successors have been made responsible for explanation the numerous ordinances, stories and matters pertaining to belief. Thus, the holy Prophet has introduced the whole Islam by referring to the two weighty souvenirs.
Therefore, traditions (Ahadit) are the fundamental pillar for understanding Islam, and have been introduced on par with the holy Qur’an.
(4) Our time is separated from the holy Prophet’s time by 15 centuries. Nobody during our time lived or experienced the events during that era. As was pointed out earlier, the only rational, reliable, and accessible reference for understanding religion is the transmitted narrations, the top-most being the holy Qur’an and the Prophet’s Sunnah. Apart from the Qur’anic text, the Muslims have two ways for gaining access to the events of that era:
First: The way selected by the Sunnis by following the caliphate system.
Second: The path pursued by the Shias in following the Ahl’ul-bayt and infallible Imams (a.s.).
We know that both groups possess books on hadith, Tafsir (interpretation of Qur’an) and history. The book named“Sahih” by Bukhari, Moslem, Tirmidhi, and Nesaee; another named Musnad by Ahmad, etc belong to the Sunnis. While Kafi, Basaer al-Darejat, Tahzeeb, Estibsar, Man-La-Yahzoro’-Faqih etc are compilations of the Shias.
If a Hadith is narrated by both groups, through the same narrator, that narrator is considered reliable by both groups, and we name him/her as a narrator having mutual approval. However, if a narrator is unacceptable by one of the groups, he is considered as“disputed” narrator.
(5) While the Shias consider the holy Imams and Hazrat Fatemah (a.s.) as the narrators having mutual approval, and the Sunnis consider them as“reliable and truthful” narrators. The Shias also believe that they are divinely gifted with the position of infallibility, Wilayat (divine authority) and Imamate (divine leadership). Thus, their narration about the Prophet’s era is considered as reliable by both groups. So, if anyone from either group had lived during any of these Imams’s time, would have accurately traced the Prophet’s era without any distortion and acquired the commandments and other matters with full confidence.
(6) Consequently, in the Shia culture, the period for examining the narrators is about 250 years (from the holy Prophet’s era till the martyrdom of Imam Askari). Now, the chain of transmission of the narrated Hadiths should be analyzed in the length of about 1150 years (starting from today and going back to 260 A.H.). On the other hand, the Sunnis should examine them in the length of more than 1400 years (counting from today going back to the Prophet’s demise). As a result, there exists more reliability in the chain of narration of Shia narrators (provided the parameters for correctness of hadith are the same).
If we take into account the divine position of Imams as well, then the whole issue would change drastically. This is because its no secret that their knowledge is linked to the Prophet’s knowledge as well as the holy Qur’an and their immaculate status is confirmed by the Qur’an. Besides, the Shia scholars possess special precision and parameters with regards to narrators because of their inclination towards the school of immaculate Imams (a.s.). For example, parameters like conformity of Hadith with reason, their non-contradiction with the holy Qur’an, or other widely transmitted Hadith.
(7) We accept that there exist weak traditions too. But their presence cannot affect the credit of thousands of authentic and reliable traditions. Is not in the Sunni collection of traditions any weak tradition? A review of Sahih-Moslem and Sahih-Bukhari would give its reader an idea about the extent of traditions that exists in non-Shia books, that contradict the holy Qur’an, reason, or other widely transmitted traditions. In this connection, you may refer to“Elm’ul-hadith” (Zain-ul-Abedeen Qorbani, pages 349- 375),“Sairi-dar-Sahihain” (Najmi, third section, pages 66- 73) and“Azvao-lal-Sunnat-ul-Muhammadiah” (Mahmood Aburiah).
Just for the sake of good luck, we shall now set forth a hadith concerning Imamate of Amir-ul-Mu’minin (a.s.) and about Hazrat Mahdi (a.t.f.s.)
The holy Prophet (s.a.w.a.) said:
“Of whomsoever I am his master (Maula), Ali is his master too.”
(Ehtejaj: Tabarsi: 58-67)
Also, Abu-Zar said: Allah’s messenger (s.a.w.a.) said:
“The one who obeys my command has obeyed Allah’s command; and the one who disobeys me has disobeyed Allah; the one who obeys Ali has obeyed me, and the one who disobeys him has disobeyed me.” 
About Hazrat Mahdi (a.t.f.s.) the holy Prophet said:
“Ali is from me; his spirit is from my spirit, and his clay from my clay. He is my brother, and I am his brother. He is my daughter’s husband, the lady who is the chief of the ladies from the first to the last. The two leaders of my nation, the two masters of the youth of paradise viz., Hasan and Husain, and nine offspring from Husain are all from Ali. The ninth from them is “the Qaem” who will fill the earth with equity and justice, just as it would have been filled with injustice and tyranny.” 
Similarly, the messenger of Allah said:
“The land shall overflow with injustice and tyranny. Then, a man from my progeny shall rise. He will fill it with equity and justice.” 
We see the Shia, as well as, the Sunni traditions throw light on the Imamate and Wilayat of Ali (a.s.), and Mahdaviyat and Qaemiyat of Hazrat Mahdi (a.t.f.s.).
To sum up:
1. The innate and intellectual way open to man concerning the past era and generation is narration and traditions only.
2. This is the only solution in all the dimensions whether it is history or sciences, or doctrines or precepts.
3. In narrating Islamic and religious realities, the only reliable references are the holy Qur’an and traditions.
4. The structure and arrangement of the holy Qur’an shows that it requires interpretation, explanation and commentary by the teachers of Qur’an (the holy Prophet and immaculate Imams).
5. By adhering to the divine interpreters, the Shias pursue the path of Sunnah and traditions.
6. Today, if we wish to acquire the realities of religion and the true interpretation of the Qur’an, we must follow Ah’l al-bayt and their traditions only.
7. About Imamate and Wilayat, as well as, Mahdaviyat and Qaemiyat, we must search for them in the Qur’an and traditions of Ah’l al-bayt.