The German theologian Paul Tillich (1886–1965) is renowned today for his powerful synthesis of Christian theology and existentialism. He released an acclaimed series of short books written during the 1950s, including the evocative titles The Courage to Be and Dynamics of Faith. These texts laid out Tillich’s dynamic theology with a rare combination of economy and mystery, memorably describing “faith as a state of being ultimately concerned” and declaring that “courage can show us what Being truly is.” Later, he authored an epic three-volume Systematic Theology, which dove deep into the murk of existentialist philosophy, famously arguing that God constitutes the ultimate “ground of Being” implied in humanity’s search for self-transcendence.

While Tillich has become a veritable giant within contemporary theology, many are not familiar with his lifelong commitment to socialism, in both theory and practice. Tillich was active in Germany’s religious socialism movement and became deeply conversant with Marxist theory and politics. Notably, he authored a lesser-known book, The Socialist Decision, in which argued for the necessity of socialism in the twentieth century — and which he deemed his best work.

Socialism was no mere academic matter for Tillich. He served as a chaplain during World War I, an experience that brought him face-to-face with the catastrophes of capitalism and militarism, as well as the political anemia of the Christian churches. He returned home to his native Germany, which was quickly turned upside down by the 1918 November Revolution. Kaiser Wilhelm II’s empire gave way to the cultural roller-coaster of the Weimar Republic, and Tillich and his second wife, Hannah Werner-Gottschow, embraced its social liberalism and experimentalism. They lived in an open marriage and frequented the avant-garde venues and social circles of the time.