Timothy Johnson, a familiar face to millions of people as medical editor for ABC-TV, was approaching his 65th birthday. Something huge and mysterious was tugging at him to revisit the theological questions he had examined so intensely as a young seminary student.

There was a catalyst to the urge. Decades of conversations with secular colleagues in both medicine and media—two disciplines rife with skeptics—had challenged him.

"They would always ask me, 'So, Tim, what do you really believe?'" Johnson said in an interview. "'I mean, if you had to write it down, what would you say?' And I thought maybe I should try to write it down."

As someone who had distanced himself from some labels and givens of institutionalized Christianity, Johnson needed to explain, as much to himself as to others, what he believed. The result was a book that quickly found its way into The New York Times top 10 Hardcover Advice Bestseller List.

That's the Advice list, not the religious list; neither Johnson nor IVP aimed the book at the Christian market. Yet Finding God in the Questions amounts to an informal apologetic.

An informal apologetic, sales indicate, is just what the doctor ordered for postmodern masses. Johnson does not pretend to present anything more than his mortal quest—no overweening, absolute truth claims here—an earthy endeavor well-suited to his engaging, self-effacing tone. Something curious happens along the way. The gospel comes ringing through, gently as a bell choir.

Can a gospel without any overweening truth claims be any good? Consider Johnson on his own terms. A would-be clergyman who opted instead for medicine, his concerns go beyond the eternal destiny of hidden tribes who have never heard of Jesus.

First, he takes on the existence ...