Sufism, the religious philosophy of Islam, is described in the oldest extant definition as the apprehension of divine realities, and Muhammadan mystics are fond of calling themselves Ahl al-Haqq, the followers of the Real. The central doctrines from this point of view, have been drawn to some extent on materials collected during the last twenty years from a general history of Islamic mysticism-a subject so vast and many-sided that several large volumes would be required to do it anything like justice. Here, a sketch is drawn in broad outline on certain principles, methods, and characteristic features of the inner life as it has been lived by Muslims of every class and condition from the eighth century of our era to the present day...
The Sufi who sets out to seek God calls himself a 'traveler (salik), he advances by slow stages (maqamat) along a 'path' (tariqat) to the goal of union with Reality...

Reynold Alleyne Nicholson (1868-1945), was the greatest Rumi scholar in the English language. He was a professor for many years at the Cambridge University, in England. He dedicated his life to the study of Islamic mysticism and was able to study and translate major Sufi texts in Arabic, Persian, Ottoman Turkish. That a Western "scholar of the first rank" dedicated much of his life to the study and translation of Rumi's poetry was very fortunate.
His monumental achievement was his work on Rumi's Masnavi (done in eight volumes, published between 1925-1940). He produced the first critical Persian edition of Rumi's Masnavi, the first full translation of it into English, and the first commentary on the entire work in English. This work has been highly influential in the field of Rumi studies, world-wide. His critical Persian text has been re-printed many times in Iran and his commentary has been so highly respected there, that it has been translated into Persian (by Lahuti, 1995).