"For the medieval Muslim, the significance of heresy was religious: it was related, that is to say, to differences of belief, opinion, or practice concerning divinity, revelation, prophecy, and matters deriving from these. These matters, in Islam, extended to include the whole range of public and political life, and any further explanation, beyond the religious one, was unnecessary, even absurd, for what could be added to the greatest and most important of all the issues confronting mankind? The grounds and terms of argument between opposing religious factions were almost invariably theological. That is not to say that Muslim polemicists always accepted the good faith of their opponents. Very often they accuse those whose doctrines they dislike of pursuing ulterior motives—but usually these ulterior motives are themselves religious. The commonest of them is the recurring theme of a plot to undermine Islam from within in favor of some other faith. This is usually connected with some more or less fabulous figure, of superlative malignity and perversity, who functions as a diabolus ex machina, to explain dissension and heresy in the community. This is in part due to the general tendency of Islamic historical tradition to attribute to the limitless cunning and multifarious activity of an individual the results of a long development of thought and action; in part also to the tactic, familiar in other times and places, of discrediting critics within the community by associating them with enemies outside the community...
The medieval European, who shared the fundamental assumptions of his Muslim contemporary, would have agreed with him in ascribing religious movements to religious causes and would have sought no further for an explanation. But when Europeans ceased to accord first place to religion in their thoughts, sentiments, interests, and loyalties, they also ceased to admit that other men, in other times and places, could have done so. To a rationalistic and materialistic generation, it was inconceivable that such great debates and mighty conflicts could have involved no more than “merely” religious issues. And so historians, once they had passed the stage of amused contempt, devised a series of explanations, setting forth what they described as the “real” or “ultimate” significance “underlying” religious movements and differences. The clashes and squabbles of the early churches, the great Schism, the Reformation, all were reinterpreted in terms of motives and interests reasonable by the standards of the day—and for the religious movements of Islam too explanations were found that tallied with the outlook and interests of the finders.
To the nineteenth century, obsessed with the problems of liberalism and nationality, only a struggle for national liberation could adequately explain the religious cleavage in Islam, the bitter controversies between doctrine and doctrine, the armed clash of sect with sect. The intuition of Gobineau and Renan, the insight of Dozy and Darmesteter helped to create a picture of Shi'ism as a liberal revival of the Persian national genius, as a resurgence of the Aryanism of Iran in generous revolt against the alien and committing Semitism of Arabian Islam...
Nevertheless this hypothesis is now generally abandoned. Wellhausen, Goldziher, Barthold and others have shown that the main centers of early Shi‘ism were among the mixed, predominantly Semitic-speaking population of southern Iraq; that Shi‘ism was first carried to Persia by the Arabs themselves and for long found some of its most enthusiastic supporters there among the Arab soldiers and settlers, and in such places as the Arab garrison city of Qum—even today one of the most vigorous centers of Shi‘ite religion in Persia. Though ethnic antagonisms played their part in these struggles—and the nineteenth-century scholars made a lasting contribution in discerning them—they were nor the sole or even the most potent factor. The accusations of the early polemicists are directed against the old Persian religion, not against the Persian nation—and the charges of Iranian dualist infiltration can be paralleled by similar tales of Jewish and Christian attempts to insinuate their own doctrines into Islam under the cover of Islamic heresy. It was in North Africa, Egypt, and Arabia that Shi‘ism won its earliest and mosr resounding political successes. Only two of the important independent dynasties of Muslim Persia professed the Shi‘ite religion...
The advance of knowledge and of understanding thus brought the abandonment of a theory which in any case had ceased wholly to satisfy. For the twentieth century, in the West at least, the problems of nationality and national liberation were no longer the main themes of the historic process. The expansion and contraction of societies, the clash of interests and classes, economic change and social upheaval, class war and cataclysm—these were the basic truths which the twentieth-century historian saw in the mirror of history. Kharijism, Shi‘ism, and the other movements in Islam were now interpreted in terms nor of national but of social categories, not of race but of class. In the first quarter of the twentieth century, the Russian progressive Barthold, the German conservative Becker, the Italian positivist Caetani, the French Catholic Massignon looked around them and achieved a new understanding of the revolutions of early Islam—both of those that succeeded and of those that failed...
It has been observed as a curiosity that the word “religion” does not occur in the Old Testament. This is not because the ancient Hebrews had no religion but because they did nor distinguish a separate part or compartment of their personal and public lives for which they might require this special term. Religion embraced the whole of life—man’s dealings with his fellow men, with society and with the state, as well as his dealings with God. Even the simple, basic acts of working and resting, eating, drinking, and procreation were sanctified as the fulfillment of a divine command and a divine purpose. Islam too has no words to distinguish between sacred and profane, spiritual and temporal, for it does not accept or even know the dichotomy that these pairs of antonyms express—the cleavage and clash of Church and State, of Pope and Emperor, of God and Caesar. The Islamic State is in theory and in the popular conception a theocracy, in which God is the sole source of both power and law and the sovereign His viceregent on earth. The faith was the official credo of constituted state and society, the cult the external and visible symbol of their identity and cohesion, and conformity to them, however perfunctory, the token and pledge of loyalty. Orthodoxy meant the acceptance of the existing order; heresy or apostasy, its criticism or rejection. The same sacred law, coming from the same source and administered through the same jurisdiction, embraced civil, criminal, and constitutional as well as ritual and doctrinal rules. The sovereign was the supreme embodiment of the Holy Law, maintained by it and maintaining it. Where Church and State are inextricably interwoven, so too are religion and politics, and religion provided the only possible expression, in public and social terms, of sustained opposition. Whenever a group of men sought to challenge and to change the existing order, they made their teachings a theology and their instrument a sect, as naturally and as inevitably as their modern western counterparts make ideologies and political parties."
--- The Significance of Heresy in Islam in Islam in History: Ideas, People, and Events in the Middle East / Bernard Lewis (also published as Some Observations on the Significance of Heresy in the History of Islam in Studia Islamica)