the importance muslims attached to the qur'an

As we have pointed out above, the verses and chapters of the Qur'an were in oral use amongst Muslims at the time of its first and second compilation into one volume. They were extremely careful in preserving what they had learnt by heart.
Moreover, a large group of companions and their followers were engaged only in recitation and learning the Qur'an by heart. The collecting together of the Qur'an into one volume took place under their scrutiny. They all accepted, without objection, the volume when it was given to them and then made copies of it.
It happened that when some men tried to record verse 34 in "Repentance," "And those who hoard up gold and silver" without the "and" in the 'Uthmanic (second compilation) volume, they were prevented from doing so. The companion Ubayy ibn Ka'b swore that if anyone left out the "and" he would fight him with the sword.
As a result, the word "And" was recorded. One day the second Caliph, during the time of his own caliphate, read the verse, And the first to lead the way of the Muhajirin and Ansar and those who follow them in goodness. [IX:100], without the word "and"; he was opposed and forced in the end to read it with the "and".
The Qur'an that had been compiled by 'Ali was rejected by several people when he showed it to them. Despite this, Ali made no objection or resistance and accepted the Qur'an in circulation for as long as he lived, even during the time of his own caliphate.
Likewise, the Imams of the Prophet's family, the successors and sons of the Prophet, did not mention their objection to the Qur'an to the intimates amongst their Shiah followers. They always referred to the Qur'an in common use and in their commentaries and ordered the followers to recite it as the people did.
Ali's silence in the matter of the difference of order between the two volumes was in keeping with the preference of the Shiah Imams for commentary of the Qur'an by the Qur'an; for them the order of the Medinan and Meccan chapters has no influence on the meanings of the Qur'an; commentary of each verse is made by comparing it to another group of verses.
Moreover the Qur'an is eternal and valid for all times and places; such local and temporary particularities as this time, place and circumstances of revelation can have no effect on the higher scale of meanings contained in the qur'an.
It is true that there are benefits to be gained by knowing certain details of revelation; they help one to discern the development of divine wisdom, social laws or stories of the past prophets and nations; also an understanding of the reasons for revelation show how the call to Islam progressed during the twenty-three years of the prophet's mission.
We would like to make clear, however, that it was in order to preserve the unity of the Muslims that caused the Shi'ites to be silent in this matter.