This was because...
This was because, on the one hand, about two thirds of Quranic verses were seen to deal with doctrines, social principles, higher ethical values, historical events relating to past messengers and their peoples, and accounts of their struggle against the oppressors and taghuts of their times; on the other hand, though the remaining one-third of them relate to legal matters (such as: salat, sawm, khums, zakatt, Hajj, jihad, al-'amr bi al-maruf wa al-nahy `an al-munkar, tawalli, tabari; legal contracts and economic deals, such as matters relating to marriage, divorce, will and inheritance, sale, lease and mortgage; penal matters, such as those relating to hudud, diyat and qisas; matters relating to government, judiciary, judgement, testimony, qualifications for judgeship; matters relating to the rights of parents, debts, etc.) they deal mostly with general principles, leaving the details and particulars to the Sunnah in accordance with the verse: Take whatever the Apostle brings you, and abstain from whatever he forbids you from.(59:7) The Quran as the Source of Law It may be argued that the Quran and some traditions expressly state that the Quran contains everything and that there can be no shortage while we possess the Quran.
Accordingly, it may be said, there is no reason why the Ahl al-Sunnah should have faced any difficulty in deducing ahkam after the Prophet's demise.
In reply to this, we should say that it is undoubtedly true that: (not a thing, fresh or withered, but it is in a Book Manifest), but the belief that everything has been mentioned in the Quran and that nothing has been omitted by it, in accordance with the verse: (We have not omitted anything in the Book) does not imply that everyone, regardless of his qualifications, is capable of obtaining the pearls lying in the depths of its shoreless oceans.
The belief that the Quran contains all the ahkam and is capable of answering every question that can be raised by man does not conflict with the view that an extraordinary level of knowledge, effort and learning is essential for obtaining all the ahkdm of the Shari'ah from the Quran' and for finding the answer to any question.
Thus we find that some traditions that expressly declare that there is everything in the Quran also add that it is not possible to understand part of Quranic meanings without reference to someone who is infallible (Masum). Usul al-Kafi (vol. I, p. 62)records the following statement of Amir al-Mu'minin (A) in this regard:.