Hoping to reverse a trend that has seen millions convert to Protestant alternatives or abandon religion altogether, the pope urged Latin Americans to "be faithful disciples, so as to be courageous and effective missionaries."
But defence of the faith and the fight for social justice are not to be confused with political engagement, he said, in a clear reference to liberation theology, a movement that remains popular across the region beset by a growing disparity between rich and poor, violence, drug trafficking and corruption.
"The Church is the advocate of justice and of the poor, precisely because she does not identify with politicians nor with partisan interests," he said.
Benedict, opening a conference of Latin American and Caribbean bishops in the sanctuary town of Aparecida, said: "Faced with new and difficult choices, the faithful are looking to this fifth conference for renewal and revitalisation of their faith in Christ."
Alternately stern and gentle over his five-day stay, his first to the Americas since his election two years ago, the 80-year-old German pontiff railed against abortion, hedonism and sex out of wedlock while lauding Latin Americans' "great thirst for God."
Up to a million people flocked to an open-air mass in Sao Paulo on Friday when Benedict created Brazil's first saint, Franciscan monk Antonio de Sant'Ana Galvao, as part of a strategy to reverse major inroads that evangelical faiths have made in the Latin American region.
Largest Catholic concentration
Brazil, with a population of nearly 190 million, has the world's largest concentration of Catholics, but their numbers have fallen in the past decade, from 74 to 64 percent of the population, while the ranks of the evangelists have swelled from 11 to 17 percent, according to a recent survey.
The Catholic Church has especially lost ground in Brazil's megacities where an influx of people from the countryside to low-income suburbs and slums have been drawn to the alternative offered by sects that are highly active there.
But Pentecostal churches were stung when Benedict charged on Friday that they are using "aggressive" recruiting tactics.
The pope had said that people who are "insufficiently evangelised most vulnerable to the aggressive proselytising of (evangelical) sects ? a just cause for concern."
Benedict said such people "are easily influenced because their faith is weak, confused, easily shaken and naive, despite their innate religiosity."
On Sunday the pontiff spoke of "new pseudo-religious phenomena" as an additional drain on the Church as he tasked the bishops with finding "new paths and creative pastoral plans."
The bishops' conference, which will close on 31 May, is a "great gathering (that) opens up a future of hope for the Latin American family," the pope said.
The pope urged Catholics to rebuild through example, saying "the Church does not engage in proselytism. Instead, she grows by attraction ... she accomplishes every one of her works in spiritual and practical imitation of the love of her Lord."
'Not a political ideology'
Benedict said the Christian faith is "not a political ideology, not a social movement, not an economic system," in an urging that appeared aimed at proponents of liberation theology, popular across Latin America where it emerged in the 1970s.
The movement stresses Christ as the liberator of the oppressed and emphasizes the Christian mission to bring justice to the poor, particularly through political activism.
As the Vatican's chief doctrinal enforcer for more than two decades before becoming pope, Cardinal Jospeh Ratzinger led a campaign to stifle the movement, and as recently as March a leading exponent of liberation theology, Jesuit priest Jon Sobrino, was warned over his writings.
Abortion was an especially sensitive issue during the papal visit, since Brazilian President Luiz Inacio Lula da Silva said his government views it as a public health issue.
The pope also devoted a large part of a youth rally on Thursday defending marriage, premarital chastity and faithfulness between spouses, in a country with notably relaxed sexual mores.