All Praise to Allah Subhanahu wa Taala and blessings of Him be on Prophet Muhammad peace be upon him His family and companions,
Why the work of the mujtahid Imams of Sacred Law, those who deduce shari‘a rulings from Qur’an and hadith are important and the question arises "Who needs the Imams of Sacred Law when we have the Qur’an and hadith? Why can’t we take our Islam from the word of Allah and His Messenger (Allah bless him and give him peace), which are divinely protected from error, instead of taking it from the madhhabs or "schools of jurisprudence" of the mujtahid Imams such as Abu Hanifa, Malik, Shafi‘i, and Ahmad, which are not?"
To simplify it Nuh ha meem keller mentioned this incident
I had a visitor one day in Jordan, for example, who, when we talked about why he hadn’t yet gone on hajj, mentioned the hadith of Anas ibn Malik that
the Messenger of Allah (Allah bless him and give him peace) said, "Whoever prays the dawn prayer (fajr) in a group and then sits and does dhikr until the sun rises, then prays two rak‘as, shall have the like of the reward of a hajj and an ‘umra." Anas said, "The Prophet (Allah bless him and give him peace) said: ‘Completely, completely, completely’" (Tirmidhi, 2.481).
My visitor had done just that this very morning, and he now believed that he had fulfilled his obligation to perform the hajj, and had no need to go to Mecca. The hadith was well authenticated (hasan). I distinguished for my visitor between having the reward of something, and lifting the obligation of Islam by actually doing it, and he saw my point.
But there is a larger lesson here, that while the Qur’an and the sunna are ma‘sum or "divinely protected from error," the understanding of them is not. And someone who derives rulings from the Qur’an and hadith without training in ijtihad or "deduction from primary texts" as my visitor did, will be responsible for it on the Day of Judgment, just as an amateur doctor who had never been to medical school would be responsible if he performed an operation and somebody died under his knife.
The mujtahid Imams were thus explainers, who operationalized the Qur'an and sunna in the specific shari'a rulings in our lives that are collectively known as fiqh or "jurisprudence". In relation to our din or "religion", this fiqh is only part of it, for the religious knowledge each of us possesses is of three types. The first type is the general knowledge of tenets of Islamic belief in the oneness of Allah, in His angels, Books, messengers, the prophethood of Muhammad (Allah bless him and give him peace), and so on. All of us may derive this knowledge directly from the Qur'an and hadith, as is also the case with a second type of knowledge, that of general Islamic ethical principles to do good, avoid evil, cooperate with others in good works, and so forth. Every Muslim can take these general principles, which form the largest and most important part of his religion, from the Qur'an and hadith.
The third type of knowledge is that of the specific understanding of particular divine commands and prohibitions that make up the shari'a. Here, because of both the nature and the sheer number of the Qur'an and hadith texts involved, people differ in the scholarly capacity to understand and deduce rulings from them. But all of us have been commanded to live them in our lives, in obedience to Allah, and so Muslims are of two types, those who can do this by themselves, and they are the mujtahid Imams; and those who must do so by means of another, that is, by following a mujtahid Imam, in accordance with Allah's word in Surat al-Nahl,
" Ask those who recall, if you know not " (Qur'an 16:43),
" If they had referred it to the Messenger and to those of authority among them, then those of them whose task it is to find it out would have known the matter " (Qur'an 4:83),
in which the phrase those of them whose task it is to find it out, expresses the words "alladhina yastanbitunahu minhum", referring to those possessing the capacity to draw inferences directly from the evidence, which is called in Arabic istinbat.
These and other verses and hadiths oblige the believer who is not at the level of istinbat or directly deriving rulings from the Qur'an and hadith to ask and follow someone in such rulings who is at this level. It is not difficult to see why Allah has obliged us to ask experts, for if each of us were personally responsible for evaluating all the primary texts relating to each question, a lifetime of study would hardly be enough for it, and one would either have to give up earning a living or give up ones din, which is why Allah says in surat al-Tawba, in the context of jihad:
" Not all of the believers should go to fight. Of every section of
them, why does not one part alone go forth, that the rest may gain
knowledge of the religion and admonish their people when they return,
that perhaps they may take warning " (Qur'an 9:122).
The slogans we hear today about "following the Qur'an and sunna instead of following the madhhabs" are wide of the mark, for everyone agrees that we must follow the Qur'an and the sunna of the Prophet (Allah bless him and give him peace). The point is that the Prophet (Allah bless him and give him peace) is no longer alive to personally teach us, and everything we have from him, whether the hadith or the Qur'an, has been conveyed to us through Islamic scholars. So it is not a question of whether or not to take our din from scholars, but rather, from which scholars. And this is the reason we have madhhabs in Islam: because the excellence and superiority of the scholarship of the mujtahid Imams--together with the traditional scholars who followed in each of their schools and evaluated and upgraded their work after them--have met the test of scholarly investigation and won the confidence of thinking and practicing Muslims for all the centuries of Islamic greatness. The reason why madhhabs exist, the benefit of them, past, present, and future, is that they furnish thousands of sound, knowledge-based answers to Muslims questions on how to obey Allah. Muslims have realized that to follow a madhhab means to follow a super scholar who not only had a comprehensive knowledge of the Qur'an and hadith texts relating to each issue he gave judgements on, but also lived in an age a millennium closer to the Prophet (Allah bless him and give him peace) and his Companions, when taqwa or "godfearingness" was the norm--both of which conditions are in striking contrast to the scholarship available today.
Now if someone is not following a particular madhab then scholars say that he is specifically following his nafs where he finds his nafs happy he sticks to that so eventually following his nafs.All imams are same in aqeedah but differ slightly in fiqh so following one particular madhab makes confusions out of the minds make easy to follow commands of Allah Swt simplifying to follow the shariah.
Abu Huraira reported: Allah's Messenger (may peace be upon him) as
saying: If the din were at the Pleiades, "Even then a person from Persia"
would have taken hold of it, or one amongst the Persian
descent would have surely found it.(Muslim)
Imam Jalal ud-din as-Suyuti (rah) who is renowned to be Mujaddad of 9th century said of this hadith
I say this hadith has glad tiding for Imam Abu Hanifa May Allah be pleased with him.
see also this http://seekershub.org/ans-blog/2009/08/13/how-can-a-convert-follow-a-school-of-thought-correctly/
Allah Swt and His Messenger knows best.