At an open-air Mass in Écône, Switzerland, before a crowd of about 16,000 people, four priests became bishops last month. The men professed their fidelity to tradition against “heretics, schismatics, and those who rebel against our Holy Father.” They did so knowing full well that, in becoming bishops, they lacked something the Catholic Church deems essential: permission from the pope.All four of these men are members of the Society of Saint Pius X, or SSPX, an arch-traditionalist group of clergy founded in 1970 by the French archbishop Marcel Lefebvre. For decades, SSPX has battled with the Vatican over the group’s fear that, as one theologian told me, “in reading the signs of the times, the Catholic Church is more beholden to the times than she is a light to the nations.” Now tensions have reached a breaking point.The Vatican warned SSPX before the Écône Mass that consecrating bishops without a papal mandate would be considered a “schismatic act,” a formal separation from the Catholic Church. After the Mass, the Church issued a decree saying that the new bishops, plus the two who ordained them, incurred an automatic excommunication: They can neither receive communion nor celebrate licit Masses nor officiate valid marriages and confessions. The 700 or so SSPX priests worldwide will also fall into schism, and thereby be excommunicated, if they remain with the society. Even lay churchgoers who “formally adhere” to the group may face the same sanction.[Read: The real religious ‘renewal’ happening in Gen Z]By some estimates, 25,000 people in the United States are affiliated with SSPX—a tiny fraction of the roughly 53 million American Catholic adults. Many Catholics may not even know that the Church finds itself in arguably its largest schism since the 19th century. Nonetheless, the SSPX excommunications touch on broader disputes in Catholicism today: about reform, orthodoxy, and whether the Church’s institutional changes of the past half century have been for the better. That is, this schism is about more than just SSPX. It’s also about how the Church will respond to a larger group of traditionalists—those who, though still Catholic, have questioned or even attacked many of the beliefs and practices that characterize the faith today.SSPX’s fight with the Catholic Church began as a response to the Second Vatican Council, or Vatican II, the most pivotal event of 20th-century Catholic history. From 1962 to 1965, the Church instituted a series of reforms that reimagined its role in a secular age. Perhaps most famous was the council’s overhaul of the Mass in hopes of increasing participation among the faithful. In most Masses, priests stopped facing the altar and began facing the people. The local language replaced Latin as the main tongue of worship. In some parishes, out went Gregorian chants and in came guitars.Vatican II also reformed the doctrine of extra ecclesiam nulla salus, or “outside the Church, there is no salvation.” As Larry Chapp, a former theology professor at DeSales University, told me, the council clarified that Catholics “have to be open to the movement of grace outside of the boundaries of the Church.” Guided by this vision, Vatican II produced writings that promoted religious freedom, ecumenical efforts with other Christians, and “dialogue and collaboration” with non-Christian religions.To SSPX, these changes were calamitous. The society’s 28-page profession of faith asserts that true Catholicism rejects ecumenical and interfaith dialogue, and states that other faiths are “false religions” and “the work of the devil.” SSPX also holds fast to the pre–Vatican II Traditional Latin Mass as the only legitimate liturgy: The profession of faith declares that the vernacular Mass “favours heresy, weakens the faith,” and “turns the faithful away from the adoration due to God.”Lefebvre participated in Vatican II himself—he even signed all of the writings that SSPX now objects to. But he soon started denouncing the council’s reforms. Five years after the council concluded, he founded SSPX with the mission of training priests in preconciliar beliefs and practices. In 1974, Lefebvre condemned Vatican II for contributing to “the destruction of the Church,” one of the many accusations and acts of defiance that prompted Church authorities to revoke his permission to run the society. Lefebvre kept recruiting priests anyway. By 1988, SSPX had approximately 200 clergy worldwide, mainly in France, Switzerland, and the United States. In June of that year, Lefebvre ordained four priests as bishops, ignoring Pope John Paul II’s orders not to. The pontiff excommunicated Lefebvre and the four bishops but declared no formal schism. Lefebvre, for his part, continued leading the society—and vehemently opposing Vatican II, which he described as the “adulterous marriage of the Church with liberal ideas”—until his death in 1991.[Read: The first Millennial saint]The Vatican let SSPX exist in a kind of limbo state in the years after the 1988 excommunications. Members of the society were officially limited in the sacraments that they could officiate, but SSPX kept ordaining priests and holding illicit Masses. And yet they were still, technically, a part of the Catholic Church. Church leaders, Chapp said, made “efforts to bring them back into the fold.” In 2009, Pope Benedict XVI lifted the excommunications of the four living SSPX bishops that John Paul II had effected two decades prior. A few years later, Pope Francis granted SSPX priests permission to hear confessions and officiate marriages. Still, SSPX has no interest in being part of a Church that doesn’t spurn Vatican II. The society holds that the council’s reforms create a “state of necessity” that allows it to do what it must “to preserve the faith.” This is the irony at the heart of SSPX’s theology: The society claims to be a bulwark of the Catholic faith; it also dismisses the pope’s authority as the final interpreter of that faith. “This is not a trivial issue,” Chapp said. “Staying in union with the vicar of Christ is a central defining feature of what it means to be Catholic.”Although SSPX considers itself a lone defender of tradition, other prominent Catholics—including popes—have expressed concerns about the liturgy and emphasized the importance of doctrinal clarity. Before his pontificate, Pope Benedict XVI worried that Vatican II’s liturgical changes, as implemented, had in some situations downplayed the “authentic inner vibrancy” of the Mass. John Paul II was a consistent proponent of interfaith dialogue, but nonetheless cautioned in 1990 against “a religious relativism which leads to the belief that ‘one religion is as good as another.’”But these popes—and many other Catholics who have raised questions about the implementation of certain Church reforms—were working within the Church, not against it. SSPX, by contrast, “doesn’t have to wrestle with unclarity or ambiguity,” Father Gregory Pine, a professor of moral theology at the Dominican House of Studies in Washington, D.C., told me. It doesn’t do the hard theological work of interpreting new teachings alongside tradition. It simply maintains a posture of rejection—and calls it orthodoxy.It’s one thing for a tiny sect to go rogue. But traditionalism has many supporters in the broader Catholic Church—which means that how the Church moves forward has implications not only for SSPX but also for this larger set of traditionalists, and for the unity of the Church as a whole.Like SSPX, some traditionalists have been viciously critical of the pope, especially during Francis’s pontificate. On a 2024 visit to Singapore, for example, the late pontiff met with an interfaith group of youth and said that “all religions are paths to God”—an off-the-cuff comment that reflected a Vatican II teaching that non-Christian religions “often reflect a ray of that Truth which enlightens all.” Still, several prominent Catholic traditionalists denounced Francis. One said that he spouted “heresy that flies in the face of Jesus Christ.” Another created a video titled “Pope Francis Is a Heretic Denying Tradition, Part 2” that echoed arguments SSPX had made before. The Traditional Latin Mass also has a following beyond SSPX. Roughly 1 million American Catholic adults attend it weekly, which is just 2 percent of the country’s overall Catholic adult population but still many more people than are affiliated with the society.The SSPX excommunications contain a clear message to all traditionalists: Vatican II itself is not up for debate. The council’s teachings and reforms are essential components of the faith, not optional addenda to it. Some Catholics believe that the Church should also continue its official position of limiting access to the Traditional Latin Mass. The Catholic writer Mike Lewis told me that support for the liturgy tends to come with an “entire theological structure” that questions the authority of Vatican II and, by extension, the pope.[Read: What the fastest-growing Christian group says about America]Father Pine, however, said that some proponents of the Traditional Latin Mass are simply looking for a liturgy that is “celebrated worthily” and at a “transcendent register.” And some Church leaders have signaled an openness to the Traditional Latin Mass in the weeks since the excommunications. Archbishop Salvatore Cordileone—whom Pope Leo XIV recently appointed to the Vatican’s highest court—has called for “more access” to the liturgy, and some U.S. bishops have promoted it as part of their pleas to SSPX’s followers to return to the Church.Leo XIV has stressed unity since he became pope, last year, and he has not made his position on the Traditional Latin Mass fully known. In excommunicating SSPX, he rebuked a small group of the most vocal supporters of the Traditional Latin Mass. But he has also met with a well-known proponent of the liturgy, as well as with the authors of a forthcoming book that argues that Traditional Latin Mass–goers aren’t the recalcitrants their critics make them out to be.Excommunication, the theologians I spoke with told me, serves a dual purpose: It’s punitive, but it’s also medicinal, meant to call a person or group back to communion. SSPX’s lay members, by early indications, plan to remain in schism for the time being. Those who return, though, may well find their Church to be a bit more open to traditionalism than they imagined it would be.