Instead, the Pope said, peace and justice in this world require a divinely inspired change in the human heart.

"When addressing the deeper dimension of personal and community life, human strategies will not suffice to save us," the Pope said in his homily during an outdoor Mass at Guanajuato Bicentennial Park March 25. "We must have recourse to the one who alone can give life in its fullness, because he is the essence of life and its author."

Echoing his earlier critiques of liberation theology, a Marxist-influenced movement that found prominent supporters among Latin American Catholics during the 1970s and '80s, Pope Benedict told reporters accompanying him on the plane from Rome that the "church is not a political power, it is not a party ... it is a moral reality, a moral power."

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Yet the Pope made it clear that he was not encouraging believers to withdraw into a private kind of piety uninvolved with worldly affairs.

"The first job of the church is to educate consciences," he said, "both in individual ethics and public ethics."

Christian hope, the Pope told an audience that included Mexican President Felipe Calderon, does not merely console the faithful with the promise of personal immortality.

The theological virtue of hope, he said, inspires Catholics to "transform the present structures and events that are less than satisfactory and seem immovable or insurmountable, while also helping those who do not see meaning or a future in life."

The practical expression of this inspiration, the Pope said, is the church's extensive charitable activities, which help "those who suffer from hunger, lack shelter, or are in need in some way in their life."

That point seemed particularly relevant to the second half of Pope Benedict's Latin America visit, to Cuba March 26-28, where he was to mark the 400th anniversary of the country's Virgin of Charity of El Cobre.

Catholic charities in Cuba have become notably active in recent years, sometimes in cooperation with agencies of the state. After half a century of communist government and decades of official atheism there, Pope Benedict could hardly find more powerful evidence for the inadequacy of secular solutions than the church's growing role in caring for Cuba's poor.