Summoned by a new pope whose watchword so far has been “mercy,” hundreds of bishops from around the world will gather in Rome on Sunday to begin debating whether the Catholic Church should alter course and warmly embrace divorced and remarried Catholics.

Having heard their advice, Pope Francis alone will decide what changes, if any, are possible. And that will not happen until after an even larger global meeting at the Vatican resumes the discussion next year.

But the battle lines are drawn: A handful of powerful cardinals have already trumpeted their opposition. They warn that greater hospitality to remarried Catholics would effectively undo the church’s teaching on the permanence of marriage at a time when marriage is already under extraordinary stress.

Significantly, however, it is Francis who called the meeting — a pope who last year said the church should see itself as a “field hospital” for life’s wounded. And a Vatican working document to guide the two-week meeting, technically called an “extraordinary synod,” reports that many bishops around the world have told the Vatican they want the church to offer remarried Catholics “mercy, clemency and indulgence toward new unions.”

Catholic teaching holds that couples validly married in the church are married forever. Civil divorce is permissible, but not remarriage. Those who do remarry commit adultery and are cut off from the Eucharist, the sacramental symbol of community at the center of Catholic life.

“While they belong to the church and are certainly invited to participate in the life of the church, they are asked to exclude themselves from communion, because communion is a sign of being in union with the teaching of the church,” Archbishop Gregory Aymond said.

Aymond said not even Francis is free to change church teaching on marriage, but he is free to enlarge the scope of “pastoral care” of Catholics in difficult situations, essentially offering “workarounds” that can ease burdens without reversing core teachings.

Francis last week announced the formation of a commission to streamline a classic “workaround,” the Catholic annulment process, Aymond said. Slow, cumbersome and frequently controversial, that process nonetheless frees divorced Catholics to marry if the church finds that their first marriage was in some way canonically defective.

“So he’s ahead of the synod in a sense, and the synod hasn’t even started,” Aymond said.

Other issues on agenda

The synod — composed of one bishop from each country, plus influential members of the Vatican bureaucracy — actually will discuss more than remarriage. It will consider other ways the church can reach out to families confronting issues of abortion, same-sex unions and contraception.

But remarriage after divorce has seized the spotlight thus far, because traditional Catholic marriage, which the church regards as both a sacrament and the fundamental social institution, is under tremendous pressure.

Cohabitation is routine. Almost 40 percent of engaged couples seeking a Catholic wedding in metropolitan New Orleans have been living together, according to figures Aymond supplied the Vatican in 2011.

And marriage is down. In the 1970s, nearly three-quarters of the U.S. adult population were married, while in 2012, only about half were married, according to researcher Mark Gray at CARA, a social research center affiliated with Georgetown University.

When marriage does occur, fewer than 8 percent of all U.S. weddings occurred in Catholic churches in 2011, despite the fact that Catholics are a quarter of the population.

Finally, the number of divorced Catholics has more than doubled since the 1970s, according to CARA. While the increase is leveling off, and the divorce rate among Catholics is 8 percentage points lower than for the general population, almost 6 million Catholics have experienced divorce — and if remarried, or married to a divorced spouse, they are cut off from the center of Catholic life, according to Gray.

Given that grim reality, “Some say there is room here, without changing the teaching, for pastoral care,” Aymond said.

Cardinals at odds

But going into the synod, a number of influential cardinals have publicly faced off on behalf of clashing agendas.

One side is led by German Cardinal Walter Kasper, who has proposed that a remarried Catholic might be readmitted to the Eucharist if he or she repents the failure of the first marriage, has ruled out a return to that marriage, cannot abandon the responsibilities of the second marriage without adding to the human damage, is trying to live the second marriage “on the basis of faith” and has a desire for the sacraments.

But some powerful Vatican voices are opposed to that. Cardinals Gerhard Mueller, head of the Vatican’s doctrinal office, and Raymond Burke, an American who heads the Vatican’s highest court, have published essays on the eve of the synod arguing that changes like those Kasper envisions would effectively reverse Jesus’ admonition in Mark’s Gospel that “what God has joined together, no human being must separate.”

Meanwhile, critics inside the church bemoan the paradox that several hundred ordained, celibate men will discuss the plight of modern families. By contrast, only 14 married couples have been invited to attend, and they are observers with limited input.

But to prepare for the meeting, the Vatican sent a long questionnaire about family life in their countries to bishops around the world. In many cases, bishops forwarded them to local Catholics and asked them to speak up.

Aymond had the questionnaire posted online and in the New Orleans archdiocesan newspaper, the Clarion Herald. “We didn’t get an overwhelming response,” he said. And reviewing the results, he said, the hospitality to potential changes on matters like same-sex marriage, contraception and divorce “included every possible stance, from the extremes to the middle.”

“It was very, very diverse,” he said.

Problem not with teachings

Like other bishops around the world, Aymond forwarded his findings to the Vatican, which incorporated them into the planning document that will guide the synod’s conversations.

Significantly, that document asserts that couples’ struggles with issues around marriage, fertility and related subjects are largely due to the church’s failure to properly educate them on its teachings, not the teachings themselves.

Still, the synod may provide an opening for some change, not least because, unlike his predecessors who sent staff representatives, Francis will attend and immerse himself in the discussions, Aymond said.

It was Francis who earlier this year called an Argentine woman who had sought his advice and told her that she could receive the Eucharist despite her marriage to a divorced man, the woman’s husband said. The Vatican has said it will not comment on the conversation because it was confidential.

And speaking to reporters on his return from a trip to Brazil last year, Francis said of remarried Catholics: “I think this is the moment for mercy.”

Referring to Francis’ metaphor of the church as a “field hospital,” Aymond said the pope will “be walking in the field.”

“I’m sure he will feel that pain and empathy and will incorporate that into his pastoral care,” he said.