On March 15, former senator Rick Santorum delivered a passionate speech at the annual Conservative Political Action Conference. Republicans can’t abandon social conservatism and traditional American principles merely for the sake of electoral convenience, he said. “Permit me to paraphrase a great teacher and ask, ‘What does it profit a movement to gain a country and lose its own soul?’” Santorum’s line garnered applause from the CPAC audience, who instantly recognized his reference to a famous line from the Gospel of Mark.

The irony is that Santorum’s allusion is far more familiar to contemporary Americans than to our ancestors. It was the Old Testament, not the New Testament, containing the Gospels, which guided Americans up to the Civil War. That is the persuasive central argument of American Zion, the erudite new book by Eran Shalev. An historian at Haifa University in Israel, Shalev scrutinizes letters, speeches, newspaper articles, handbills and books to illustrate the tremendous power the Old Testament held over the early years of the United States. The Republican Party and the religious right consistently urge a return to what they believe is America’s first principles, but those principles had little to do with the teachings of Jesus Christ.

Europeans are often mystified at the religiosity of Americans. However much atheism may be gaining ground, America is still far more religious than other economically-advanced societies, thanks to our earliest settlers. The Puritans “saw themselves as Israelites fleeing a new Egyptian captivity,” Shalev writes, “crossing a seat to reach freedom and taking possession of a promised land.”

It is not novel to observe that Americans are religious. But the content of American religious belief—the way they have fused biblical beliefs with nationalist myths—is distinctive. Settlers in the young country believed quite literally that Israel’s second coming was in the New World. Even deists such as Thomas Jefferson and Benjamin Franklin reimagined the revolution as an “Exodus-like deliverance from slavery,” notes Shalev. Just as the first Israelis were to a light under the world, so too have Americans been convinced that they must be a “redeemer nation,” in the words of Ernest Lee Tuveson.

But slavery transformed the religious debate. It became more difficult to see America as uniquely designed as a new Israel in the bloody wake of the Civil War. Slaveholders and their supporters pointed out that slavery was practiced by God’s chosen people, the Hebrews. But they also progressed to use the New Testament in pointing out that Jesus never criticized slavery. The advocates of slavery used the New Testament, and Shalev says this “was in itself innovative and forward-looking.”

On the opposing side, William Lloyd Garrison, radical abolitionist and co-founder of the Anti-Slavery Society, argued that his followers were ostracized and oppressed in a manner similar to what Jesus and his early Christian followers suffered. Indeed, the masthead of Garrison’s newspaper carried an image of Jesus, “the Liberator.” John Brown, the abolitionist hero, or terrorist—or both—justified his raid on Harper’s Ferry by saying that the New Testament teaches “that all things whatsoever I would that men should do to me, I should do even so to them. It teaches me even further, to ‘remember them that are in bonds, as bound with them.’”

Slavery was not the only reason the New Testament gained popularity in the 19th century. The Second Great Awakening, by which millions of Americans were caught in a wave of evangelical revivals more attuned to Christ and the redemption, accounts for at least as much. But the conflict over” our peculiar institution” forwarded the shift to a New Testament-directed conversation.

After the Civil War, the Old Testament never regained its prominence in American myth. Shalev claims that before 1800, Christianity in America was not “a Jesus faith.” Such a situation is virtually impossible to imagine now, so entwined is American Christianity with the story of Jesus Christ and his mission. American exceptionalism is routinely referred to by politicians and intellectuals, but the once-common notion that this exceptionalism meant that the U.S. is a reincarnated version of ancient Israel is virtually non-existent.

And yet, the widespread belief that America has a mission to bring democracy to the world—a notion introduced at the policy level by Woodrow Wilson and maximized rhetorically by George W. Bush—is in many ways a secular version of the national beliefs popular prior to the Civil War. It is a testament to the power of American religious views that they can be transmuted into secular terms—virtually divorced from God—with little change in actual policy.

It also helps explain why political disputes in America are so bitter. Consider that when Canada’s Supreme Court ruled in late 2004 that same-sex marriage was constitutional, there were few protesters outside the courtroom. In the U.S. this week, conversely, thousands warred over the issue, frequently describing their respective positions in apocalyptic terms. Indeed, everyday issues from taxation to gun control to health care are frequently discussed in religious terms, as if the fate of the universe depends upon the specific level of Amtrak funding. But if one recognizes that Americans see their country in religious terms, the level of acrimony is more easily understandable. If nothing else, Shalev’s convincing book reaffirms G. K. Chesteron’s notion that America is a nation with the soul of a church.