Universally recognized as the "father of Pietism" and considered perhaps the single most important German religious figure since Martin Luther, Philipp Jakob Spener achieved this significance neither through theological genius nor an extraordinary personality. Rather he stands at the threshold of the age when, as F. Ernest Stoeffler puts it, "Reformed and Lutheran churches ... lost touch with vital concerns of religion, concentrating their efforts on the attempt to answer questions which were no longer being asked"; and throughout a lifetime in the church he focused and fostered the impulses for reform that had been gathering for more than a century. But unlike others before him, Spener articulated his vision as a broad and coherent model of human life based on sincere Christian piety and intense self-reflection. In preaching, catechesis, and writing, he rooted his idea of reform in the experiences of a Christian life. Throughout his own life...