The Persian Sufism: "The Sufi phenomenon is not easy to sum up or define. The Sufis never set out to found a new religion, a mazhab or denomination. They were content to live and work within the framework of the Moslem religion, using texts from the Quran much as Christian mystics have used to Bible to illustrate their tenets. Their aim was to purify and spiritualize Islam from within, to give it a deeper, mystical interpretation, and infuse into it a spirit of love and liberty. In the broader sense, therefore, in which the word religion is used in our time, their movement could well be called a religious one, one which did not aim at tying men down with a new set of rules but rather at setting them free from external rules and open to the movement of the spirit.
This religion was disseminated mainly by poetry, it breathed in an atmosphere of poetry and song. In it the place of great dogmatic treatises is taken by mystical romances, such as Yusuf and Zuleikha or Leila and Majnun. Its one dogma, and interpretation of the Moslem witness: 'There is no god by God', is that the human heart must turn always, unreservedly, to the one, divine Beloved."