An extract from Shaheed Mutahhari book called "Imamat and Khilafat" on unity amongst Muslims.

We would like to say that there is no doubt that unity is the most important requirement of the Muslims, and that these old rancours are the basic cause of all troubles in the Muslim world. It is also true that the enemy is always ready to exploit these disputes. But it appears that the critic has misunderstood the concept of Muslim unity. Muslim unity which has been a subject of discussion among the scholars and the broad-minded sections of the Muslims does not mean that the Muslim sects should ignore their principles of faith and articles of acts for the sake of unity, adopt the common features of all the sects and set aside the peculiarities of all. How can this be done when this is neither logical nor practical. How can the followers of any sect be asked to ignore for the sake of preserving the unity of Islam and the Muslims, any of their beliefs or practical principles which they consider to be a part of the basic structure of Islam?
Such a demand would mean to overlook a part of Islam in the name of Islam?

We are Shi'ahs and are proud of following the chosen descendants of the Holy Prophet. We do not regard as compromisable any act which has been even slightly commended or condemned by the Holy Imams. In this regard we are not willing to fulfill the expectation of anybody, nor do we expect others to give up any of their principles in the name of expediency or for the sake of Muslim unity. All that we expect and wish is the creation of an atmosphere of good will so that we, who have our own jurisprudence(fiqh), traditions, scholastic theology, philosophy, exegesis and literature, should be able to offer our goods as the best goods, so that the Shi'ah should no more be isolated and so that the important markets of the Muslim world should not be closed to the fine material of Shi'ah Islamic knowledge.

The most prominent among those who advanced the noble idea of Islamic unity, in our times, have been the late Ayatullah Burujardi among the Shiah and Allamah Shaykh Abdul Majid and Allamah Shaykh Mahmud Shaltut among the Sunnis. But they never had such a view of Islamic unity in their mind. All that these learned men advocated was that the various Muslim sects in spite of their different theologies should on the basis of the large number of common features existing among them form a common front against the dangerous enemies of Islam. These learned men never proposed under the name of Islamic unity a religious unity which is not practical.

The main idea of the late Ayatullah Burujardi was to pave the ground for the dissemination of the knowledge of the Prophet's chosen descendants among his Sunni brethren. He believed that this was not possible without creating good will and understanding. The success he achieved in the publication of some theological books of the Shi'ah in Egypt by the Egyptians themselves was one of the most important achievements of the Shi'ah scholars.

Anyhow, the advocacy of the thesis of Islamic unity does not demand that we should feel shy of telling the facts. What is to be avoided is to do anything that may injure the feelings and sentiments of other parties. As for a scientific discussion, it relates to the domain of logic and reason, not to that of sentiments and feelings.

~ Imamat and Khilafat by Ayatullah Shaheed Mutahhari