This work investigates the fundamental nature of mystical experience by distinguishing between theistic and monistic varieties of religious consciousness. R. C. Zaehner, a distinguished scholar of Eastern religions and former Spalding Professor of Eastern Religions and Ethics at Oxford, utilizes a comparative framework to analyze these states. He argues that not all mystical experiences are identical, challenging the prevailing academic consensus of his time that sought to unify all such phenomena under a single psychological or metaphysical umbrella.

Experts frequently cite this text as a foundational, albeit controversial, critique of the reductionist approach to religious experience. Readers often note the academic density of the prose and the rigorous theological scrutiny applied to non-Western traditions.