On one recent weekday evening, I was sitting in a circle in a concrete garage praying Compline, a traditional nighttime liturgy, by candlelight. Within our small intentional community in London, we often recite these strange, rhythmic old sentences stitched together from the Psalms.

Our visitors, though, likely found them unfamiliar. Around the flickering flames, I could see a philosopher, a Marxist (and polyamorous) political theorist, a prominent feminist, a historian of ideas, and a columnist for a major magazine. None of them would call themselves Christians, but all had willingly chosen to join this nightly ritual.

Justin Brierley’s new book, The Surprising Rebirth of Belief in God, names this phenomenon, which I have experienced for several years: a new openness to spiritual matters among those we might have thought hostile. Brierley, until recently, hosted the long-standing apologetics radio program Unbelievable?, which has welcomed many serious public intellectuals. Having witnessed numerous debates between those inside and outside the church, he reports a dramatic “change in tone and substance.”

A century and a half after the poet Matthew Arnold heard the “long withdrawing roar” of the sea of faith, Brierley opens with a provocative observation: Seas don’t withdraw forever. The tides go out, and then they come back in. Brierley is betting the sea is on the turn.

As evidence, he tells the stories of several recent high-profile converts (like writer Paul Kingsnorth) and Christian-friendly skeptics (like historian Tom Holland). He spells out that many outside the church today are not acidly dismissive of faith but are curious, even wistful, for its ideas and communities. He tells these stories both to encourage believers and to warn the church against “answering yesterday’s objections, rather than engaging with those who are asking a different set of questions altogether.”

Brierley rightly ...