The British public instantly recognizes the message—a reference to the words of Shadrach, Meshach, and Abednego standing before King Nebuchadnezzer's fiery furnace. "Our God is able to save us … and if not, we will remain faithful to him anyway." The message galvanizes the British people. Thousands cross the English Channel in boats to rescue their army.

January 2001: America's newly elected President delivers his inaugural address. Commenting on it, Dick Meyer of CBS News confesses, "There were a few phrases in the speech I just didn't get. One was, 'When we see that wounded traveler on the road to Jericho, we will not pass to the other side.'"

Meyer concludes, "I hope there's not a quiz."

What a difference six decades make. For centuries, biblical references were the common coinage of Western speech. As Dunkirk demonstrates, citizens were so steeped in the Scriptures that they immediately recognized a cryptic biblical allusion. But today that memory has been erased. Consider: Pollster George Barna says only a small percentage of Americans can name the Ten Commandments, and only 42 percent can identify who preached the Sermon on the Mount. As Oxford theologian Alister McGrath explains, "In an increasingly secular culture, fewer and fewer people outside the Christian community have any real understanding of what Christians believe."

This spiritual illiteracy represents a sobering predicament for the church: How can we evangelize neighbors who no longer recognize, let alone think, in Christian ...