The autobiography Al Ghazzali wrote towards the end of his life,
The Confessions of Al Ghazzali,
is considered a work of major importance. In it, Al Ghazzali recounts how, once a crisis of epistemological skepticism had been resolved by "a light which Allah Most High cast into my breast ... the key to most knowledge," he studied and mastered the arguments of kalam, Islamic philosophy, and Ismailism. Though appreciating what was valid in the first two of these, at least, he determined that all three approaches were inadequate and found ultimate value only in the mystical experience and insight he attained as a result of following Islamic practices. William James, in Varieties of Religious Experience, considered the autobiography an important document for "the purely literary student who would like to become acquainted with the inwardness of religions other than the Christian" because of the scarcity of recorded personal religious confessions and autobiographical literature from this period outside the Christian tradition.