Jerome I. Gellman observes that the mystic experience of God's presence, a sense of having direct contact with the divine, often compels belief in God's existence. On the basis of widely accepted principles connecting appearance with reality, Gellman contends, the claims people make of having experienced God show that belief in God is strongly rational.

Such claims are sufficient in number and variety to support a line of reasoning making it rational to believe that God exists and irrational to deny God's existence. Gellman considers challenges to his thinking based on epistemological grounds as well as challenges growing out of the diversity of religious experiences across the range of world religions. He thoroughly evaluates reductionist explanations of apparent experiences of God and finds them incapable of invalidating his view.

Finally, he directs his attention to the two most compelling arguments against the existence of God: the charge that the idea of a perfect being is logically incoherent, and the threat to theism based on the existence of evil, in both its logical and probabilistic forms. Until and unless stronger objections come along, he concludes, personal experiences of God constitute sufficient evidence of God's existence.