Pope Francis called on all leaders in all fields to protect people and the environment, and to shun hatred, envy and pride as he formally began his ministry Tuesday in front of a crowd of more than 100,000 on St. Peter's Square at the Vatican.  Leaders from around the world attended, and millions watched and listened on television, radio and the Internet, six days after his surprise election. 

On a sunny spring morning, Pope Francis led the outdoor mass to mark the beginning of his papacy.

After receiving the symbols of his office, including his papal ring, he addressed what he called “all those who have positions of responsibility in economic, political and social life.”

The pope urged leaders to protect nature and all people, particularly the poorest. He said leadership and power are really about service, and that even the pope should be “lowly, concrete and faithful.”

Some analysts may interpret his remarks as serving notice on members of the Church's hierarchy who have been accused of power grabs and misconduct and those who have been shielding priests accused of sexual abuse. Many in the Church and outside are watching to see what the new pope does about the scandals. Among them is Robert Gahl, an American who is a professor of ethics at Rome's Pontifical University of the Holy Cross.

“The key thing, which is his personal stamp, which he specified already back in Buenos Aires as the archbishop there in Argentina, was to never look away when there is a problem in the diocese," said Gahl. "That the bishop is responsible for looking after especially the most vulnerable.”

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The surprise choice of the former Cardinal Jorge Mario Bergoglio of Argentina left many experts wondering how the new pope will handle his job. But those who know him claim to have a pretty good idea, including Argentine priest Eduardo Mangirotti, who got to know the pope back home.

“He is a person of action. And we are going to see not only a person who makes gestures in front of a camera, we're going to see a person of action here in the Vatican,” said Mangirotti.

But Tuesday was a day of prayer and ceremony, with leaders of Catholic denominations from around the world paying homage, leaders of other religions paying their respects, and top world officials looking on.

Still, Pope Francis has seemed to relish more the chances he has had to interact with ordinary people. As he rode through the square on an open truck before the ceremony, he waved and smiled, and stopped to kiss babies. And when he saw a disabled man in the crowd, he stepped down to give him a personal blessing. Such moments have already become a hallmark of his papacy.