Revealing links between the radical Reformation and early modern philosophers such as Baruch Spinoza and Pierre Bayle, Erdozain demonstrates that the dynamism of the Enlightenment, including the very concept of "natural reason" espoused by philosophers such as Voltaire, was rooted in Christian ethics and spirituality. The final chapters explore similar themes in the era of Darwin and Marx, showing how moral revolt preceded and transcended the challenges of evolution and "scientific materialism" in the unseating of religious belief. The picture that emerges is not of a secular challenge to religious faith, but a series of theological insurrections against divisive accounts of Christian orthodoxy.