VATICAN CITY — Pope Francis celebrated his first mass as pontiff Thursday, urging the Catholic church to emphasize its core faith and the Gospels or risk becoming like "a compassionate NGO," referring to non-governmental organizations that provide community services.
He warned that following anything other than spiritual values was like children building sand-castles on a beach, Reuters reported. "Then everything comes crashing down," he said, according to the report.
The first full day of his pontificate saw more details emerge about his character and background.
Officials said Pope Francis had declined the official papal car and joked with cardinals not long after being elected as head of the world's 1.2 billion Roman Catholics on Wednesday night.
One Vatican insider admitted he was as "surprised" by the choice of Francis as the rain-soaked crowd at St. Peter's Square — where an audible gasp followed the pontiff's unveiling.
"I didn’t expect it," press spokesman Father Federico Lombardi told reporters, referring to the moment when Argentine Cardinal Jorge Bergoglio appeared on the balcony overlooking the square.
The Latin American pope’s election shattered Europe's centuries-old grip on the papacy, and his choice of name — in honor of the 12th century saint from Assisi — is widely seen as a nod to a new era of simplicity.
Lombardi said Pope Francis declined the official papal car for his first journey from the Sistine Chapel, choosing instead to board a bus with cardinals who had just elected him.
Later, at dinner, the new pope prompted laughter by responding to their toast with the remark: "May god forgive you for what you have done."
Those observations were echoed by New York's Cardinal Tim Dolan, who told TODAY's Matt Lauer that Francis had shunned protocol that called for him to sit on elevated platform, preferring instead to stand alongside fellow cardinals. "So he greeted each of us as brothers, literally on the same level as we were.”
Francis returned Thursday to the church-run hostel where he had stayed ahead of the conclave and insisted on paying the bill.
"He was concerned about giving a good example of what priests and bishops should do," a Vatican spokesman said. He did not disclose how much the bill totaled.
A theological conservative who has also been hailed for his compassion toward the poor, the 76-year-old Francis is the first Jesuit pontiff.
He is also expected to become the first pope in more than 600 years to meet his predecessor. Francis will travel to the hillside papal summer residence at Castel Gandolfo to greet the emeritus pope, who is living there temporarily after abdicating as Benedict XVI on Feb. 28.
Lombardi on Thursday confirmed the historic meeting would take place but said the timing had yet to be decided.
Francis will be formally installed as the church's new leader on Tuesday.
Earlier Thursday, he made a quick and discrete visit to Rome’s Basilica of Santa Maria Maggiore.
"He spoke to us cordially like a father," Father Ludovico Melo told Reuters after the meeting. "We were given 10 minutes' advance notice that the pope was coming".
The new pope, who is also now Bishop of Rome, prayed before a famous icon of the Madonna called the Salus Populi Romani, or Protectress of the Roman People.
NBC News' Vatican expert George Weigel predicted Francis would "certainly" prove to be a reformer when it comes to the Roman curia — the Vatican bureaucracy at the heart of the Catholic church.
The election of Francis appeared to surprise even those at the very heart of the church leadership, particularly among its sizable Italian contingent.
The Conference of Italian Bishops was so confident of victory for Milan’s Cardinal Angelo Scola that an emailed press statement congratulating the new pope was sent with a covering email that referred to Scola, not the victorious Bergoglio, as the chosen successor to Benedict.
Italian newspaper La Repubblica reported that the conclave had "rebelled against the curia."
However, Cardinal Dolan denied the conclave had been divided. "I didn't sense that tug of war at all," he said. "I sensed a rather remarkable consensus. We needed a man who had a good track record of sound, effective pastoral governance, and we got what we wanted."
Italy's La Stampa newspaper cited an interview Bergoglio gave last year in which he condemned "vanity" and said being cardinal was "not an award to be bragged about."
Outside the Vatican, torrential overnight rain had cleansed St Peter's Square of any sign of the 100,000-strong crowd that had cheered, applauded and cried when Francis emerged on the balcony above.
Newspaper vendors were kept busy by tourists lining to see inside the basilica.
"I think he will be a pope who thinks about more than just the Vatican," said Maryland native Marjorie Steiner, 61, who visited St. Peter’s Square on Thursday as part of a vacation in Rome.
Dory Gordon, 51, from Houston, Texas, who was also on vacation, said: "As a Catholic I'm really excited that they have made this break with tradition. It sends out a good message that the church is here for all the world's people."
NBC's John Newland, Reuters and The Associated Press contributed to this report.