The choice of day to anoint him as the holy father of the Roman Catholic Church carries a rich symbolism: It is the day that Catholics celebrate the Feast of St. Joseph to honor Jesus' father on Earth, the carpenter Joseph. It also happens to be Father's Day in Italy.
Foreign dignitaries and heads of state are welcome to attend but by tradition don't receive a specific invitation, Lombardi said.
U.S. Vice President Joe Biden is to lead the U.S. presidential delegation for the Mass, the White House said Friday, with House Democratic Leader Nancy Pelosi also among the party. On Friday, House Speaker John Boehner, a Republican, said he will send a separate bipartisan congressional delegation.
On Saturday, Francis will give an audience to the media. He will probably hold Mass on Sunday, then deliver the traditional Angelus, one of the most common Catholic prayers, the spokesman said.
Palm Sunday is just a week later, and the new pontiff will be busy, as it is the holiday that kicks off Holy Week, which culminates in Easter celebrations.
A new direction
Rosica, the Vatican spokesman, said that Francis was making his own mark as the 266th pope -- and shaking things up a little.
As head of the church, the Argentine is following the same path he took during his years as archbishop in Buenos Aires, he told CNN.
"He was a pastor there, very close to the people, and he's continued that -- he's simply changed the color of his robes right now, and the world is paying attention to every move, every word, every gesture," Rosica said.
"Those of us who were used to him in Buenos Aires are not at all surprised with this, but I can tell you that it does send some jolts through the system here, which is so deeply rooted in tradition and beautiful ceremonies and following the Book.
"Pope Francis is telling us that the Book is very important, but there's even something more important: Be faithful, be close to the people, smile and take things as they come."
Lombardi, in the news briefing, gave a similar message. "We are all learning how to behave around the holy father. We don't have instructions yet from him on how he wants to be treated," he said.
Rosica said the media's focus on the scandals surrounding the church missed the point of why Francis was elected as pope.
"The cardinals chose someone who is a model of holiness, they chose someone who has a real passion for evangelization ... which is more than just a buzzword, this is what the church is all about.
"They chose someone who has an extraordinary record for compassion, for relating to people not just within the Catholic Church ... but those on the fringes, the poor, the destitute, the disenfranchised, those living in irregular relationships, those who have suffered, those who have brought suffering upon themselves."
'Put faith first'
Francis set the tone for his vision of the church's future in his first Mass as pope Thursday, held in the Sistine Chapel with the cardinals who participated in the conclave.
With solemnity, he delivered a short, unscripted homily about moving the Catholic Church forward, saying its leaders must put faith at the heart of what they do -- or risk it becoming nothing more than a charity.
"We can walk as much as we want, we can build many things, but if we do not profess Jesus Christ, things go wrong. We may become a charitable NGO, but not the church, the bride of the Lord," he said.
"When we are not walking, we stop moving. When we are not building on the stones, what happens? The same thing that happens to children on the beach when they build sandcastles: Everything is swept away, there is no solidity."
After the Mass, the seals were ceremonially removed from the doors of the papal apartment at the Vatican, although renovation work must be done before Francis moves in. The apartment was sealed after Benedict XVI's departure two weeks ago.
Pope of firsts
When Jorge Bergoglio stepped onto the balcony at the Vatican on Wednesday evening to reveal himself as the new leader of the world's 1.2 billion Catholics, he made history as the first non-European pope of the modern era, the first from Latin America, the first Jesuit and the first to assume the name Francis.
He takes charge of a global flock at a time when confidence in the church has been dented by revelations of sex scandals and corruption claims.
A group representing the alleged victims of sexual abuse by priests wrote an open letter Francis on Thursday, requesting a meeting.