Le Pen’s success in the recent round of voting for France’s next president, which will go to a run-off on Sunday, marks a resurgence of nationalist populism in the country. While religion isn’t necessarily driving French policy debates or voting behavior, Le Pen’s campaign illustrates how nominal religious values can be used as an argument for closed borders and stronger national identity.

The National Front has always had a mixed religious identity. In the early days of the party, which was founded by Marine Le Pen’s father, Jean-Marie Le Pen, “fundamentalist Catholics … were a moderately strong tendency within the party,” said Rogers Brubaker, a sociologist at the University of California, Los Angeles. But “there were also … anti-Christian paganists” in the party, he added, and “those who were indifferent to religion and much more concerned about immigration.”

For his part, Jean-Marie is known as a Roman Catholic. He was the one who chose Joan of Arc as the party’s mascot. (This year, during the National Front’s annual May Day pilgrimage to a statue of the French warrior in Paris, he memorably screamed, “Help, Jeanne D’Arc!” as he laid a wreath at her feet.) In 2012, his granddaughter Marion Maréchal-Le Pen became the youngest representative to the French parliament in modern history, and she has represented the more traditionalist Catholic wing in the National Front.

And yet, Marine has made clear the divisions between her party and the Catholic Church. In an interview with the Catholic magazine La Croix, she said she is “angry with the Church, because I think that it interferes in everything except what it should really be concerned with.” The pope’s call for European leaders to take in migrants and refugees “asks that states go against the interests of their own people,” she argued. “I don’t get involved with what the pope should say to his followers. I don’t think religions should tell the French people how to vote.”

Le Pen does invoke religion, however, when she’s trying to declare who the French are and are not—specifically when she’s talking about Islam, Brubaker said. “This is a Christianism—not a substantive Christianity,” he argued. “It’s a secularized Christianity as culture … It’s a matter of belonging rather than believing.” He thinks Le Pen’s brand of Christianity as a form of identity has emerged in response to widespread Muslim immigration into the country over the last 10 or 15 years: In her view, “We are Christians,” Brubaker said, “precisely because they are Muslims. Otherwise, we are not Christian in any substantive sense.”

In 2002, Jean-Marie Le Pen made it to the run-off in the French election, shocking many. He earned an explicit rebuke from the French council of bishops: The clergy urged voters to reject the National Front candidate largely because he had denied or underplayed the significance of the Holocaust. At the time, the archbishop of Paris was Jean-Marie Lustiger, whose Polish Jewish parents had been deported to concentration camps by the Nazis during World War II.