But monastic influences at the turn of the millennium led to the adoption of a celibacy requirement at the First Lateran Council of 1123, and that tradition has held ever since. It is not doctrine or dogma, but instead a code of canon law that essentially reasons that priests unburdened by spouses or children are both more reflective of Christ and devoted to pastoral demands.

Francis, who has made clear that he sees little possibility for allowing women to be priests, called the vocation crisis an “enormous problem.”

The issue is less a question of theology than arithmetic.

In the United States, there are now about 2,500 Catholics per priest, compared with 851 per priest in 1972, according to the Center for Applied Research in the Apostolate, which is affiliated with Georgetown University.

The chasms are far wider in Africa, Asia and Latin America, where the faithful can go months without access to a priest and married deacons are increasingly called on to conduct the business of parishes. In Brazil, according to the center, there are roughly 8,000 Catholics per priest.

The Rev. Thomas J. Reese, a Jesuit priest and senior analyst for The National Catholic Reporter, said that in the face of such a crisis, the church had to decide whether upholding the celibacy rule was worth depriving the faithful of Mass and confession, which can only be performed by priests. He said that while the pontiff’s most recent predecessors had hoped for a turnaround in the diminishing numbers of priests, Francis seemed eager to push the issue.

“This is now an open topic in the church today,” Father Reese said, “whereas under John Paul II or Benedict, you could not talk about this.”