Cultural Christians. Captive Christians. American Jews. Pantheists. Muslims. Spiritual Skeptics. Mormons. The U.S. can be broken down into seven main faith groups, according to the pollster George Barna in his latest book — “The Seven Faith Tribes” — which is at least his 40th. Even he may have lost count. “These have more to do with lifestyles and values and draws parallels with faith inclinations,” Barna said in a recent phone interview from his office in California, where he oversees The Barna Group, a research organization. The faith groups are not the nation’s seven largest but are rather clusters of...