Pope Francis was to address cardinals from around the world Friday following his stark warning that the Church risked becoming just another charitable organisation if it strayed from its true mission.
The new head of the world's 1.2 billion Catholics was to kick off the day with a speech in the ornate 16th-century Clementine Hall in the Apostolic Palace at the Vatican.
Former cardinal Jorge Mario Bergoglio, the first Latin American and Jesuit pope, has rejected papal fineries and called for a return to the Church's roots.
On Thursday, he warned that the troubled Catholic Church risks becoming little more than a charity with no spiritual foundations if it fails to undergo renewal.
At his first mass with the cardinals who elected him, the Argentinian said that the Church could "end up a compassionate NGO".
He warned the cardinals against "the worldliness of the Devil".
"Walking, building and confessing are not so easy. Sometimes there are tremors," said the pope, who warned the cardinals against "the worldliness of the Devil".
Bergoglio had begun his reign by demanding to be treated as an ordinary pilgrim, in a sign that simplicity of faith may lie at the heart of his papacy.
After laying a bouquet of flowers in homage to the Virgin Mary in a basilica, Francis walked out to greet the crowds and placed his hand on the belly of a pregnant woman.
He prayed at the altar of St Ignatius of Loyola, the founder of the Jesuit order to which he belongs before returning to the priests' quarters where he stayed before the conclave and insisted on settling his own bill.
The election of the son of an Italian emigrant railway worker, who was considered a rank outsider, was met with widespread surprise and expressions of hope for change in a Church riven by scandal and internal conflict.
His elevation was also seen as recognition of the Church's power in Latin America, which now accounts for 40 percent of the world's Catholics, while it is in decline in Europe.
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.
The Vatican revealed that, for the ride back to the conclave lodgings after Wednesday's election, Francis shunned the papal limousine with the "Vatican City State One" number plates and instead boarded a minibus with the cardinals.
It was in keeping with his image as a man who as archbishop of Buenos Aires chose to live in a modest apartment rather than the official residence and took buses to work.
Francis, formerly archbishop of Buenos Aires Jorge Mario Bergoglio, has already made his mark in Rome with his informal style.
Experts said they expected the new pope to shake up the Vatican, where poisonous rivalries within the Curia -- its governing body -- plagued the papacy of Francis's predecessor Benedict XVI.
Benedict, 85, abruptly ended his eight-year papacy last month saying he lacked the strength to deal with the rigours of the job.
The Vatican confirmed that Francis had part of a lung removed as a boy, but insisted that he is in good health.
The new pope is the first non-European pontiff in nearly 1,300 years and the first from the Society of Jesus order, or the Jesuits, known for their work in education and promotion of social justice.
He was only 36 when he was named to lead Argentina's Jesuits, a job he held for six years under the country's 1976-83 military dictatorship.
The future pope and other Catholic clergy were lambasted by leftist critics for failing to act against Argentina's "Dirty War" during which 30,000 people died or disappeared.
Australia's most senior Catholic cleric spoke out Friday on the issue of Pope Francis's role under the junta, saying the controversy was based on "a smear and lie".
Sydney Archbishop George Pell, one of the men who took part in the conclave to elect the new pope, told Australian radio that "those stories have been dismissed years and years ago."
More recently, the new pontiff's opposition to gay marriage and contraception has brought him into conflict with the Argentine government of President Cristina Kirchner.
The Argentinian of Italian descent, who is the church's 266th pope, faces the immediate challenges of stamping his authority on the Vatican machinery and trying to coax back worshippers who are deserting congregations across the West.
The sexual abuse of children by paedophile priests stretching back decades cast a dark shadow over the conclave, which included several cardinals implicated in the scandals.
Francis's inauguration mass will take place on Tuesday -- a significant date in the Catholic calendar because it is the Feast of St Joseph, who is patron saint of the universal church.