Henry David Thoreau is famous for the literary excellence of his political and nature writings. But his friend Harrison Blake understood that the "true significance of [Thoreau's] life" was in fact spiritual, and he presciently asked the then-little-known Thoreau for guidance in finding a path of his own. The result was a regular exchange of letters for the remaining thirteen years of Thoreau's life, charting the evolution of his skills as a writer and thinker. The possibilities and limits of spirituality, the role of vocation in developing one's spiritual life, the importance of a direct relationship between the individual and God - Thoreau discusses these and more in his letters to Blake. The fifty letters, assembled and annotated here for the first time in their own volume by Bradley P. Dean - who has made the editing of Thoreau's manuscripts his life's work - are by turns earnest, oracular, witty, playful, practical, and deeply insightful and inspiring.