Cardinals gather for a mass at the Vatican in 1963. Later that year, Church bishops would vote to create a new mass liturgy, which largely ended the use of Latin in Catholic masses.Luigi Felici / AP

As a visitor to the United States, Pope Francis faces a minor challenge: His English isn’t so great. Over the course of the trip, he’ll give 18 speeches, and only four of them will be in English; he’ll mostly use his native language, Spanish, to give homilies and addresses.

But at Wednesday’s mass in Washington, D.C., at which Francis will canonize Father Juniperro Serra, he’ll add another linguistic twist. The main prayers of the service, along with the celebration of the Eucharist—the part of the service when people take communion—will be in Latin.

Latin! This is an exclamation-mark-worthy fact for a few reasons. “It’s very unusual,” said Father John O’Malley, the Georgetown University professor and author of What Happened at Vatican II. “It’s not unheard of, but it doesn’t make much sense, if you’re in an English parish, or a Spanish parish, to do it in Latin.”

Before the mid-to-late 20th century, Latin was a standard feature of Roman Catholic masses: Priests used it throughout the service, including for prayers and the celebration of the Eucharist. The version of the service used in Catholic churches around the world had been ratified in the mid-16th century at the Council of Trent (thus the name: the Tridentine Mass), with a few small updates made here and there.

But in 1970, a new version of the liturgy was published: Pope Paul VI’s Missale Romanum. By that time, the Church had started allowing the use of local languages in all parts of the mass. The decision to do so had been made at the Second Vatican Council: In the decree Sacrosanctum Concilium, the bishops voted to make the mass more accessible to regular Catholics by simplifying the liturgy, encouraging more participation in the service, and allowing the use of the vernacular, among other things.

Like most things that happen in the Church, this shift was symbolically complicated. Over the past 50 years, the use of Latin has become a marker of Catholic traditionalism, and in the years following the release of the new liturgy, the older version of the mass—often called the Latin or old-rite mass—became something of a political football. At first, the Holy See granted several priests and organizations the right to use the Latin mass. But by the late 1970s, the number of permissions dwindled, particularly as a conservative group of priests, led by a Frenchman named Marcel Lefebvre, pushed for the revival of the Tridentine mass. In 1984, Pope John Paul II hedged this, excommunicating the traditionalist agitators but encouraging more widespread permission to use the old-rite mass. In 2007, Pope Benedict XVI took the Church further, calling the Latin liturgy an “extraordinary form” of the mass, declaring the old and new versions “two usages of the one Roman rite,” and decreeing that priests no longer had to ask permission to use the Latin liturgy. He also encouraged priests to study Latin and learn how to give mass in the “extraordinary” form.

In some ways, this back-and-forth over the Latin mass was a way of re-litigating the ideological battles of the Second Vatican Council, which pitted traditionalists against those who wished to bring aggiornamento, or a spirit of up-to-date-ness, to the Church. (The up-to-date-ness folks largely won.) That’s why it’s so interesting that Francis has chosen to include Latin in his D.C. mass: For the most part, his papacy hasn’t been framed in this broader ideological tug-of-war. “He’s the first pope in 50 years not to have participated in the Council,” O’Malley said. “That’s good, because he’s not fighting the battles of the Council.”

The mass that will be celebrated in D.C. on Wednesday is not the pre-Vatican II mass. The service will include English, Spanish, and several other languages, according to a Vatican spokesperson, and the pope won’t be following the Tridentine liturgy. O’Malley was skeptical that the choice to include Latin is a sign of a traditionalist revival. “I think it can be interpreted that way, if you’re looking for that kind of a pointer,” he said. “But I don’t think that’s where it’s pointing.”

More likely than not, the decision to use Latin in the mass is a matter of comfort: The pope isn’t very good at English and he’ll already be speaking a lot of Spanish, so the mass offers an opportunity to incorporate another language into this visit. But it’s a small reminder that no move the pope makes come without complicated history—and symbolism—attached.

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