But there is more to the pope’s action than kindness to an 81-year-old man. In a remarkable turnaround, liberation theology is being brought in from the cold. During the Cold War, the idea that the Catholic Church should give “a preferential option for the poor” was seen by many in Rome as thinly disguised Marxism. Pope John Paul II, who had been brought up under Soviet bloc totalitarianism, was determined to crack down on it. On a visit to Nicaragua, he famously wagged a finger at Father d’Escoto’s fellow priest and cabinet minister, Ernesto Cardenal. The Vatican also silenced key exponents of liberation theology, and its founding father, the Peruvian priest Gustavo Gutiérrez, was placed under investigation by the Vatican’s guardian of doctrinal orthodoxy, the Congregation for the Doctrine of the Faith, or C.D.F.

Washington shared the Polish pope’s fears that the new theology could open another door to Communist infiltration of Latin America. The C.I.A. created a special unit that informed on hundreds of radical priests and nuns, many of whom became victims of the region’s military dictatorships.

Pope Benedict XVI took a more sophisticated approach than his predecessor. As head of the C.D.F., before becoming pope, he had issued official critiques of liberation theology in 1984 and 1986. These endorsed its advocacy for the poor but denounced “serious ideological deviations” by radicals who embraced Marxist economic determinism and class struggle. But most liberation theologians were not saying the poor should take up guns. They were saying the Catholic Church should help the poor liberate themselves from unjust economic systems through labor unions, cooperatives and self-help groups.

After the Cold War ended, Pope Benedict encouraged bishops in Latin America to find new ways of expressing the church’s “bias to the poor.” He attended their seminal meeting in Aparecida, Brazil, in 2007, at which they refined the message of liberation theology. The priest the bishops elected to draft the document was Jorge Mario Bergoglio, the archbishop of Buenos Aires, who six years later was elected Pope Francis, and announced that he wanted “a poor church, for the poor.”

The pope has gone through his own revolution on liberation theology. He was named leader of the Jesuits in Argentina in 1973, in part to crack down on the movement. But 15 years later, after undergoing what he has called a “great interior crisis,” he became “Bishop of the Slums” in Buenos Aires and revised his views. Over the following decades he rehabilitated key figures in liberation theology in Argentina and supported the kind of bottom-up initiatives that the Vatican, with its top-down authoritarian model of governance, had so feared.