In its exoteric aspect, the Keys to the Arcana preserves and transmits a wealth of information on the Holy Qur’an and its sub-disciplines. Thus, in the twelve introductory chapters, it details the history of how the text was collected, variations in the ordering of the chapters and the teaching lineages through which the text was transmitted. Then, contained within his commentary itself on each successive verse of the scripture, Shahrastani presents ample data on such aspects of the text as its grammar, semantics, and lexicography. However, it is in the esoteric aspect of Keys to the Arcana that we reach the real fruits of the author’s quest.
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Shahrastani (d.548 AH/1153 CE) is a major figure of the Islamic intellectual tradition, best known for his universal survey of religious and philosophical teachings, The Book of Religions and Sects (Kitab al-Milal wa ‘l-Nihal) and his treatment of Ash‘ari theology, The Furthest Steps in Theology (Nihayat al-Aqdam fi ‘Ilm al-Kalam).
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http://www.iep.utm.edu/s/shahras.htm