This anti-Islam rhetoric is spreading to the mainstream. The coalition government of the Netherlands requires would-be immigrants to accept progressive values before they are given a residency visa. Applicants are asked whether they tolerate the mixing of boys and girls in school, gender equality, nudity in public and gay rights. Although all applicants must take these tests, given the concerns revealed in these questions and the demographics of migration into Europe, there can be little doubt that the exams are designed to challenge adherents to Islam. Such measures are unfair to Muslims, and they violate European states’ professed commitment to multiculturalism and the separation of church and state.

What’s more, prohibitions like those on circumcision and the ritual slaughter of cattle also amount to attacks on Judaism. In France Marine Le Pen of the National Front has called for banning both the hijab and the kippah (but not the priest’s cassock) in public places. In this respect, the defense of Europe’s Christian identity is taking on an especially ugly quality: It echoes the anti-Semitic regulations of Nazi Germany and other European countries in the 1930s. So much for the Judeo-Christian roots of European culture; once again, the Jews of Europe are made to feel like foreigners.

It was only logical, if also paradoxical, then, that Jewish groups would build coalitions with Muslims. In Germany in 2012, the Jewish community rallied around the case of a Muslim family whose son’s botched circumcision became the basis for a local court to declare all circumcision unlawful. Last month the chairman of Shechita-U.K. and the deputy secretary general of the Muslim Council of Britain signed an open letter to The Daily Telegraph defending ritual slaughtering. Religious minorities that may otherwise be wary of one another are joining forces.

Will the Catholic and Protestant churches do the same? After all, since the political right’s onslaught against Islam manifests itself mostly through an aggressive form of secularism, they are collateral victims as well. The French law banning the hijab forbids all “ostentatious” religious symbols (this, in order to not seem baldly discriminatory). In Britain a 17th-century law penalizing blasphemy against Christianity was repealed in 2008 after a heated debate about whether it could be used against Salman Rushdie, the author of “The Satanic Verses.”

The political right’s dual move — claiming the mantle of Christianity but not its values — is a threat to Christianity as radical as it is indirect: It risks stripping the religion of its spirituality. In 2004 after protracted appeals in the Ludin case, which concerned the right of a Muslim teacher to wear a head scarf in school, the government of the German state of Baden-Württemberg enacted a law that banned teachers from displaying religious signs except for the “exhibition of Christian and Occidental educational and cultural values or traditions.” The same reasoning runs through the European Court of Human Rights decision authorizing the display of the crucifix in Italian schools on the grounds that it is a “historical and cultural symbol” more than the expression of any specific belief. But to defend a distinct cultural Christian identity is to secularize Christianity itself.

So far, the Christian churches have contributed to the problem. By failing to clearly distance themselves from the cultural ultranationalist right-wing parties that have co-opted the Christian idea of Europe to block the integration of Muslims, they have enabled more secularization still, as well as allowed the betrayal of religious values in the name of xenophobia.

In 2009 Cardinal Christoph Schönborn, the archbishop of Vienna, rightly criticized the populist Freedom Party of Austria for using the cross on its electoral posters: He argued that it was proffering the symbol against other religions rather than to express Feindesliebe, love for one’s enemies. Like Mr. Schönborn, the churches of Europe should reassert the fundamental values of their religions. Going beyond him, they should try to build a vast coalition with Muslims and Jews to promote the free exercise of religion, any religion.