In the early years of World War II, Britain was in its darkest hour. It stood alone, facing the "cold fury and might" of the Nazi war machine, as Winston Churchill put it. If Britain fell, Churchill said in a May 1940 radio address, the world would "sink into the abyss of a new dark age."

Hope was in short supply, God was absent from most people's daily lives, and the church was seen as irrelevant. The war was going badly, and "death was becoming a daily companion for many," writes Justin Phillips in C.S. Lewis in a Time of War.

Into this moment stepped C. S. Lewis. In his "deep booming voice" Lewis showed that God still had something to say, even in the darkest circumstances, writes Phillips in his book (first published in 2002).

In 1941, when he began giving fifteen-minute broadcast talks on BBC radio, Lewis was relatively unknown. Within four years, he would become "the most widely celebrated Christian apologist on both sides of the Atlantic," writes Phillips. The radio talks were later published as Mere Christianity.

How did this happen? Phillips, a BBC journalist who died at 49 just after completing the first draft of the book, gives much of the credit to James Welch, the BBC's director of religious programming during the war. When Welch started, BBC religious broadcasting was limited to spiritual talks by vicars and live coverage of Sunday worship. Most church leaders, Phillips says, believed that radio was beneath them. When Welch arranged for then-archbishop of Canterbury Cosmo Lang to address the nation at the beginning of the war, he hoped Lang would bring a message of hope. Instead, as Welch's assistant Eric Fenn put it, Lang's message was "completely vapid and totally irrelevant."

It appeared that in the face of the ...