Pope Francis urged South American bishops gathered at the Vatican on Monday to "speak with courage" as they address a severe priest shortage in remote areas of the region that could result in the church dropping celibacy requirements for some priests.

The three-week Synod of Bishops for the Amazon also will address crucial regional topics ranging from protection of rainforests and local cultures to climate change, migration and clean water.

"We have not come here to invent programs of social development or custody of cultures," the pope said. "We come to contemplate, to understand, to serve the peoples."

Cardinal Claudio Hummes, retired archbishop of Sao Paulo who organized the synod, said many rural Amazon communities have so little access to priests that Sunday Mass can't be held. And while the Eucharist can be distributed to worshippers by non-priests, the wafers must be blessed by a priest.

Last rites and other Catholic sacraments also are affected, Hummes said.

"Indigenous communities, faced with the urgent need experienced by most of the Catholic communities in Amazonia, requested that the path be opened for the ordination of married men resident in their communities," Hummes said. "Albeit confirming the great importance of the charisma of celibacy in the Church."

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Jim Bretzke, professor of theology at John Carroll University, says the proposal isn't really new and would not have to alter fundamental church principles. But he told USA TODAY the last two popes, Benedict XVI and John Paul II, would have likely dismissed the idea no matter how scarce priests became.

"Pope Francis, though, has shown himself to reconsidering practical issues in ways that his predecessors were reluctant to do," Bretzke said. He added that the pope, a native of South America, "perhaps is more aware of, and sensitive to, the realities of the local church there."

Pushback to the proposal will come from those already unhappy with changes demanded by the pope, Bretzke said. Francis also has warned against clericalism, or an attitude of clerical superiority embraced by some priests and bishops who see themselves as special or superior to others.

"I believe the pushback is mostly a part of a 'culture war' proxy battle in which divergent views on clericalism are being fought," Bretzke said.

The Catholic Church has required celibacy from its priests for centuries. The vows have been broken so frequently, however, that the Vatican established secret guidelines for dealing with clerics who fathered children, Vatican spokesman Alessandro Gisotti acknowledged in February.

The proposal, however, involves men who are married and have children before ordination. Francis, who hails from Argentina, is fully aware of the struggles the church faces serving its flock in the region.

Francis has said he could consider ordaining married men to address the shortage of priests. In March 2017, he told German newspaper Der Zeit that mature, married men of proven faith could possibly serve in isolated areas. He dismissed, however, giving young priests the option of rejecting celibacy.

Still, the proposal is not a lock to win the pontiff's approval.

"The pope realizes that a decision taken for one region likely will have ramifications for other regions, and this may give him pause," Bretzke said. "Also, it is clear that ultra-conservatives are fastening on this particular issue and are trying to repackage it as 'heresy' or 'dangerous,' as part of their larger agenda against the vision of the church that Pope Francis is trying to promote."