Framed most generally, The Shadow of God is a book about secularization. However, rather than treating secularization as a result of forces from outside religion—social change or the rise of science and technology, for example—it looks at it endogenously, from the point of view of the tension between faith and reason within monotheistic religion itself. This leads to the great problem of rational theology: the justification of the goodness of the world in the face of the existence of (apparent) evil.

Immanuel Kant, my book argues, developed a distinctive, “post-Lisbon” theodicy, centred on human agency and responsibility, directed towards an afterlife of reward and punishment by a just God. “It is from the necessity of punishment that the inference to a future life is drawn,” he writes.Footnote ¹ Divine justice requires that human beings know what is required of them (they must have moral knowledge) and have the ability to perform it (they must be free). Guided by this, my book presents revisionist (or, as I would prefer to say, corrective) rereadings of some of the great central themes of German Idealist philosophy: Kant's theory of freedom; the categorical imperative; Hegel's conception of Geist and history; among others.

One consequence of Kant's relentless demand for justification and its associated requirements of impartiality and transparency is that, while Kantianism overcomes the “alienation of arbitrariness,” that brings along with it the “alienation of loneliness.” There is no place in Kant's religion for divine grace or mercy: God is no longer a loving father but a stern and unyielding judge. In this way the gap between God and man is closed—morality is not imposed by God on human beings but shared between them—at the price of making God impersonal. Kant, despite not being a secular thinker, turns out, nevertheless, to be a secularizing one.

Alongside the orientation to divine judgment and the afterlife, however, we also find in Kant a conception by which human beings see themselves as participating in a shared collective project that extends through history—an “invisible church” (152). This idea of what I call “historical immortality” (142) runs through German Idealism although it is by no means confined to it. Historical immortality has had very deep consequences. Its presence is everywhere within the revolutionary, conservative, progressive, and nationalist movements of the nineteenth and twentieth centuries. By identifying these broad themes and pointing out their continuing importance, my book also aims to make a contribution to contemporary self-understanding.