"Sufism or tasawwuf, as it is called in Arabic, is generally understood by scholars and Sufis to be the inner, mystical, or psycho-spiritual dimension of Islam. Today, however, many Muslims and non-Muslims believe that Sufism is outside the sphere of Islam. Nevertheless, Seyyed Hossein Nasr, one of the foremost scholars of Islam, in his article The Interior Life in Islam contends that Sufism is simply the name for the inner or esoteric dimension of Islam.
After nearly 30 years of the study of Sufism, I would say that in spite of its many variations and voluminous expressions, the essence of Sufi practice is quite simple. It is that the Sufi surrenders to God, in love, over and over; which involves embracing with love at each moment the content of one's consciousness (one's perceptions, thoughts, and feelings, as well as one's sense of self) as gifts of God or, more precisely, as manifestations of God."