Hundreds of Catholics have been declared saints in recent decades, but few with the acclaim accorded Mother Teresa, set to be canonized by Pope Francis on Sunday, largely in recognition of her service to the poor in India.
"When I was coming of age, she was the living saint," says the Most Rev. Robert Barron, the auxiliary bishop of the Archdiocese of Los Angeles. "If you were saying, 'Who is someone today that would really embody the Christian life?' you would turn to Mother Teresa of Calcutta."
Born Agnes Bojaxhiu to an Albanian family in the former Yugoslav republic of Macedonia, Mother Teresa became world-famous for her devotion to the destitute and dying. The religious congregation she established in 1950, the Missionaries of Charity, now counts more than 4,500 religious sisters around the world. In 1979, she was awarded the Nobel Peace Prize for her lifetime of service.
Humanitarian work alone, however, is not sufficient for canonization in the Catholic Church. Normally, a candidate must be associated with at least two miracles. The idea is that a person worthy of sainthood must demonstrably be in heaven, actually interceding with God on behalf of those in need of healing.
In Mother Teresa's case, a woman in India whose stomach tumor disappeared and a man in Brazil with brain abscesses who awoke from a coma both credited their dramatic recovery to prayers offered to the nun after her death in 1997.
"A saint is someone who has lived a life of great virtue, whom we look to and admire," says Bishop Barron, a frequent commentator on Catholicism and spirituality. "But if that's all we emphasize, we flatten out sanctity. The saint is also someone who's now in heaven, living in this fullness of life with God. And the miracle, to put it bluntly, is the proof of it."
No other Christian denomination posits this notion of an individual in heaven mediating between God and humanity.
"It's not a little supernatural, it's completely supernatural," says the Rev. James Martin, S.J., whose book, My Life with the Saints, recounts his own spiritual journey. "But that's the difficulty a lot of people have with religion. The invitation is to say, 'There's something more than the rational mind can believe, and are you OK with that?' "
Roman Catholic authorities embrace the idea of miracles from heaven with such confidence that they invite skeptics to challenge them. Before candidates qualify for sainthood, the miracles attributed to them must be proven. If someone is suddenly healed after praying to a would-be saint, the Vatican has doctors verify there's no medical reason for it.
A group advocating sainthood for Marguerite d'Youville, a nun who lived in 18th century Canada, for example, sought an alternative explanation for the sudden recovery of a woman with incurable leukemia who had prayed to the nun 200 years after the nun's death. The assignment went to Dr. Jacalyn Duffin, a hematologist at Queen's University in Ontario.
Duffin agreed to do the investigation, but only after warning the group that she was not herself a believer.
"I revealed my atheism to them," Duffin says. "I told them my husband was a Jew, and I wasn't sure if they'd still want me. And they were delighted!"
The group reasoned that if Duffin, as an atheist, found there was no scientific reason the woman should have recovered, who could doubt it was a miracle? In fact, after her investigation of the woman's recovery, Duffin agreed that the woman's healing was — for lack of a better word — miraculous.
Intrigued by the experience, Duffin investigated hundreds of other miracle stories chronicled in the Vatican archives in Rome. She came away convinced that "miracles" do indeed happen.
"To admit that as a nonbeliever, you don't have to claim that it was a supernatural entity that did it," Duffin says. "You have to admit some humility and accept that there are things that science cannot explain."
A few miracle stories in recent years have involved nonmedical situations, such as when a small pot of rice prepared in a church kitchen in Spain in 1949 proved sufficient to feed nearly 200 hungry people, after the cook prayed to a local saint. More than 95 percent of the cases cited in support of a canonization, however, involve healing from disease.
Hard-core rationalists would not be likely to see such cases as evidence of a "miracle," even while acknowledging they have no alternative explanation. Devout Catholics, on the other hand, readily attribute such occurrences to God, no matter how mysterious they may be.
"In a sense, it's a little arrogant of us to say, 'Before I can believe in God, I need to understand God's ways,' " says Martin. "To me, that's kind of crazy, that we could fit God into our minds."
Canonization procedures have undergone a series of reforms in recent years. Pope Francis has instituted changes to make the promotion of a candidate less subject to organized lobbying efforts. In fact, Vatican authorities routinely interview at least a few people who doubt the suitability of someone for sainthood. (Among those contacted during the early stages of Mother Teresa's review was Christopher Hitchens, who wrote a highly critical assessment of Mother Teresa's work, calling her "a fanatic, a fundamentalist and a fraud.")
The miracles requirement has also changed over time. In 1983, John Paul II reduced the number of miracles required for sainthood from three to two, one for the first stage — beatification — and one more for canonization.
Some Catholic leaders have called for the miracles requirement to be dropped altogether, but others argue vigorously against this. Bishop Barron says that without the miracles requirement for sainthood, the Catholic Church would offer only a watered-down Christianity.
"That's the trouble with a liberal theology," Barron says. "It tends to domesticate God, make everything a little bit too neat and prim and tidy and rational. I kind of like how the miraculous shakes us out of a too-easy rationalism. We'll affirm everything great about modernity and the sciences, but I'm not going to affirm that that's all there is to life."
In one sense, the sainthood of Mother Teresa may speak to present-day Catholics in a way previous canonizations did not. Martin, editor of the Jesuit magazine America, notes that in a posthumously published collection of her private journals and letters, Mother Teresa: Come Be My Light, the nun so widely revered for her spiritual purity acknowledged that she did not personally feel God's presence.
"In my soul I feel just that terrible pain of loss," she wrote, "of God not wanting me, of God not being God, of God not existing."
Martin says Mother Teresa dealt with such pain by telling God, "Even though I don't feel you, I believe in you." That statement of faith, he says, makes her example relevant and meaningful to contemporary Christians who also struggle with doubt.
"Ironically," he says, "this most traditional saint becomes a saint for modern times."
An earlier version of this story stated that "John Paul II reduced the number of miracles required for sainthood from four to two." He reduced the number of miracles required for sainthood from three to two.