With roughly 9 in 10 of its citizens claiming to believe in God or a Supreme Being, America is widely acknowledged to be the most religious of modern industrial nations. Yet when it comes to knowledge about religion, it ranks among the most ill-informed. While close to two thirds of all Americans regard the Bible as a source of answers to life's questions, only half can name even one of the New Testament Gospels. Similarly, in a land of growing religious diversity, only 10 percent of U.S. teenagers can name the world's five major religions. Stephen Prothero, the head of the department of religion at Boston University, calls this condition a "major civic problem." His new book, Religious Literacy, tells how we got here—and how we might do better.

Were we once a religiously literate nation?

Very much so. Religious literacy and basic literacy used to go hand in hand. The Bible was the first reader of the colonists and early Americans, so as they learned to read, they read the Bible. One important sign of this literacy was that Americans conducted many of their most important civic debates, including the debate over slavery, largely in biblical terms.

You name six links in the chain of religious education that once made Americans knowledgeable about religion. What were these, and how were one or two of them weakened, if not demolished?

The big links were churches, schools, households, Sunday schools, colleges, and Bible and tract societies. In schools, the chain of memory got broken not in the '60s by secularists, as many conservative Christians claim, or by Supreme Court rulings that outlawed devotional Bible reading and prayers in public schools. Bible courses and the teaching of religion started to go away in the mid-19th century as a result of the debate over which Bible to read—and that was instigated by religious people, not secularists.

Another change was in the churches themselves, when they started focusing on loving Jesus rather than on listening to him. The Bible slowly became a kind of ornament and a source of authority rather than a book you actually read. Sermons became more about ordinary life and less about biblical narratives, while Sunday schools focused more on morality than on learning about your own particular denomination.

You say that the "United States became a nation of forgetters at the same time it became a nation of evangelicals."

Evangelicalism became the dominant religious impulse in the early 19th century, replacing Puritanism. Puritans understood God through a combination of the head and the heart. They were keen on religious learning and reason. [But] evangelicals were suspicious of the mind. Focusing on experience and emotion, they slowly turned Americans away from religious learning.

How did many Americans go from describing their civic religion as Christian to calling it Judeo-Christian?

The shift came in response, first, to the Nazis' uses of Christianity to advance their anti-Semitic program and, second, to the postwar threat of communism. In order to distance themselves from the anti-Semitic fascists and to fight "godless" communism, American Christians made common cause with Jews.