Keller begins The Reason for God with an assessment of the contemporary divide between liberalism and conservatism. Both sides are characterized by a fearful belief that the other side is in the ascendancy, and Keller suggests that both may be right, not only in politics but in religion as well. The middle of the spectrum, filled with people who are relatively ambivalent about faith, is giving way to increases on both the side of committed religious belief and the side of aggressive secularism. Globally, committed religious belief has been on a significant rise in fields as diverse as lay-level piety and academic philosophy, a rise that does not appear to be slowing. At the same time, atheism and agnosticism have likewise been gaining more adherents and more of a voice in public discourse. “In short,” writes Keller, “the world is polarizing over religion. It is getting both more religious and less religious at the same time” (xvi).

Keller shares an overview of his personal journey through doubt and faith, remarking on the curious division he noticed between different forms of Christianity as he grew up. Some Christian leaders adopted a firm doctrinal stance on the historical accuracy of the Bible and Christianity’s supernatural claims while appearing unconcerned with issues of social justice, while others seemed not to care about the truth of the Bible’s supernatural claims but put all their focus on social justice.