This work investigates the historical development, core doctrines, and philosophical underpinnings of Islamic mysticism, commonly known as Sufism. Reynold A. Nicholson, a preeminent scholar of Islamic literature and mysticism, utilizes his extensive linguistic expertise to analyze primary Arabic and Persian texts. He constructs a framework that traces the evolution of asceticism into the complex metaphysical systems that define the Sufi tradition, providing a rigorous examination of the relationship between the individual soul and the divine.

Scholars and students of Middle Eastern studies frequently cite this text as a foundational resource for understanding the intellectual history of Sufism. Readers often note the academic density of the prose, which requires a baseline familiarity with Islamic history to fully appreciate the nuanced arguments presented.