Pope Francis on Friday urged the troubled Catholic Church not to give in to "pessimism" and to find new ways of spreading the faith "to the ends of the earth".
"Let us not give in to pessimism, to that bitterness that the devil offers us every day," the 76-year-old Argentinian told an audience of the world's cardinals on his third day in office.
In a reference to the declining number of worshippers in many parts of the world, he urged the cardinals to find "the courage to persevere and also to find new ways to bring evangelisation to the ends of the earth".
Francis said he and they were "elderly", but old age brought wisdom.
"Let us give this wisdom to young people like good wine that gets better over the years," he said.
The first Latin American pope in history hailed his predecessor Benedict XVI's historic resignation as a "courageous and humble act".
Benedict, who last month became the first pope to stand down for 700 years, had "lit a flame in the depth of our hearts that will continue to burn", he said.
The new pope wore white papal vestments but also plain black shoes, not the red shoes favoured by his German predecessor, for the address in the ornate 16th-century Clementine Hall in the Apostolic Palace at the Vatican.
Jorge Mario Bergoglio has signalled his will be a more simple papacy, stripped of the fineries enjoyed by his predecessors, and has called for a return to the Church's roots.
On Thursday, he gave a stark warning that the Church, wracked by scandal and Vatican infighting, risked becoming just another charitable organisation if it strayed from its true mission.
The speeches are part of a series of events leading to his inauguration mass on Tuesday -- a significant date in the Catholic calendar because it is the Feast of St Joseph, the patron saint of the universal church.
The new pontiff is also due to meet his predecessor, who has withdrawn to the papal summer residence in Castel Gandolfo, in the coming days.
The surprise election of the son of an Italian emigrant railway worker, who was considered a rank outsider before the cardinals began their confidential deliberations, has sparked hope for change in the Catholic Church.
His elevation is also being seen as a nod to the Church's power in Latin America, home to 40 percent of the world's Catholics. In Europe, its traditional power base, it is ageing and declining.
Projecting an image as a simple man of the people, the pope chose to name himself after St Francis of Assisi, the 13th century saint who shunned the riches of his family to devote himself to God and the poor.
As archbishop of Buenos Aires, he lived in a modest apartment rather than the official residence, and took buses to work, and he has already made his mark in Rome with his informal style.
The Vatican revealed that following his election Francis had turned down a ride in the papal limousine and instead insisted on boarding a minibus with the cardinals.
But the new pope's past in Argentina, and especially his actions during its 1976-83 military dictatorship, are coming under the microscope.
Bergoglio and other Catholic clergy were lambasted by leftist critics for failing to act against the regime during Argentina's "Dirty War" in which 30,000 people died or disappeared.
Under particular scrutiny is his role in the arrest of two young Jesuits, Orlando Yorio and Francisco Jalics, who were taken to a notorious torture centre by the junta.
Bergoglio was alleged to have betrayed the young missionaries to the regime because they had become opposition sympathizers and he wanted to preserve the Jesuits' political neutrality.
For his part, Bergoglio has always denied any implication in the case of the two missionaries, and even insists he intervened with the head of the junta, Jorge Videla, to beg for their freedom.
Australia's most senior Catholic cleric on Friday defended the pope, saying the controversy was based on "a smear and lie".
Sydney Archbishop George Pell, one of the men who took part in the conclave, told Australian radio that "those stories have been dismissed years and years ago."
With health always an issue surrounding newly elected popes -- John Paul I only lived for 33 days after he was elected in 1978 -- the Vatican has confirmed that Francis had part of a lung removed as a boy, but insisted that he is in good health.
The church's 266th pope faces the immediate challenges of stamping his authority on the Vatican machinery and trying to bring back worshippers who are deserting congregations across the West.
The sexual abuse of children by paedophile priests stretching back decades also continues to haunt the Church.