A specter was haunting Columbia University on Friday – the specter of William Jennings Bryan. A daylong conference titled “Religion and Liberalism,” held at Columbia’s Casa Italiana and sponsored by the American Studies program, featured an impressive group of scholars trying to bring those difficult terms into some kind of harmony. But the gulf between religion and liberalism in contemporary American politics was on everyone’s mind, and for more than one speaker Bryan served as a perfect symbol of the divide.

Bryan, after all, was once a hero to progressives: the golden-tongued opponent of the gold standard, the defender of laborers and farmers against the power of capital, the opponent of militarism who resigned from President Wilson’s cabinet rather than take the country into the Great War. If today’s left remembers Bryan at all, however, it is as the Bible-thumping reactionary who fought Darwinism in the Scopes Monkey trial – the grandfather not of the New Deal but of the Moral Majority.

Michael Kazin, professor of history at Georgetown and author of a just published biography of Bryan, “A Godly Hero,” kicked off the conference by offering an episode from Bryan’s life as a parable of the split between religion and liberalism. In 1916, John Reed, not yet the author of “Ten Days That Shook the World” but already a radical, was sent to interview Bryan for Collier’s magazine. Reed watched as Bryan delivered passionate speeches against war and poverty, declaring, “We Americans should make the Sermon on the Mount real in the law of nations.” But this biblical language had lost the power to move a modern, urban leftist like Reed, and his profile of the great man reduced Bryan to an oafish caricature: “his hands clasped across his stomach, benevolently bringing love and order into his simple world.” Yet without the religious inspiration of a Bryan, Mr. Kazin suggested, modern liberalism is missing something crucial. It has “a big hole in the soul,” which Reed’s ideological descendants have been unable to recognize or to fill.

What to do about that hole in the soul was the no. 1 item on the agenda at Columbia. A group of speakers who unanimously identified themselves as liberals and Democrats addressed the gulf between religion and liberalism not just as an object for study but as a pressing political problem to be solved. When the novelist Mary Gordon asked, “Why are we losing and why are they gaining?” there was no need to wonder who “we” and “they” were. Much of the discussion at Columbia was about partisan political strategy – in particular, the Democrats’ fear that they cannot regain the White House without the support of white evangelicals. “Two electoral defeats,” said keynote speaker E.J. Dionne Jr., a columnist for the Washington Post, “have concentrated the liberal mind on God.”

As a result, one participant after another stressed the need for secular liberals to find common ground with believers, especially on such issues as poverty and the environment. Wilfred McClay, a professor of humanities at the University of Tennessee, denounced the left’s “failure to make common cause” with such potential allies. Most self-identified progressives today, Mr. McClay noted, find it easier to identify with H.L. Mencken, the acidulous scourge of the Bible Belt “booboisie,” than with Bryan, his frequent target. Yet Mencken, a Nietzschean elitist, was on most issues much less “progressive” than Bryan. In fact, Mr. Dionne urged, Democrats should ask, “What would Bryan do?” as a rule of thumb.

But while Democratic politics may have been the conference’s inspiration, its most valuable contributions were concerned with democratic politics in the larger sense. In fact, the very title “Religion and Liberalism” invites confusion – or at least demands interpretation – since the word “liberal” has a long and varied history.

In one of the conference’s best, most lucid presentations, Mark Lilla, of the University of Chicago, pointed out that “partisan liberals do not hold a monopoly on liberalism in the larger sense.” That larger liberal tradition began in the 17th century with theorists like Hobbes and Locke, who drew on England’s experience of religious civil war to advance a new, secular theory of government. To be a liberal in the classical sense means to believe that government is a purely human institution, based on the consent of the governed and organized according to the best lights of secular reason. As Yale’s Seyla Benhabib argued in another valuable talk, thinkers from Hobbes to Max Weber to Michael Walzer have always defined liberalism in explicit opposition to religion.

In this deeper sense, Mr. Lilla argued, American conservatives are themselves liberals. (Indeed, present-day American conservatism, with its hostility to government regulation and commitment to the free market, closely resembles the Liberal Party of 19th-century Britain.) And as Alan Wolfe, a leading sociologist of American religion, pointed out, “Liberalism has made conservative American religion possible” by keeping government from interfering in the religious sphere. It is easy to forget today, when evangelicals are increasingly assertive in politics, that Southern evangelicals were crucial supporters of the First Amendment’s separation of church and state. Members of a religious minority in the Anglican-dominated colonial South, they knew that it was the best way to guarantee their freedom of conscience.

In this more philosophical sense, the problem of “religion and liberalism” is one that should concern Americans of all parties. And not just Americans: The cartoon controversy now raging in Europe is a vital test for the future of political liberalism. It took the West centuries of religious war to learn how to disentangle politics from religion – a lesson that much of the Muslim world has not yet learned. All of America’s great strengths – our diversity, tolerance, pragmatism – finally depend on our ability to keep public reason and private belief strictly separate. That was the most important lesson learned at Columbia on Friday: that, in Mr. Wolfe’s bold but justified words, “Liberalism is the best way to organize a society that the world has ever known.”