Hundreds of thousands of Catholics and well wishers looked on as the first Latin American and Jesuit pontiff toured the square in an open-topped vehicle before the mass Tuesday, blessing pilgrims behind the barriers.
According to The New York Times, Francis — elected by a conclave of cardinals last week to take over from Benedict XVI — pledged to serve "the poorest, the weakest, the least important."
From a crimson canopy on the basilica steps, he told a crowd estimated by NBC to be around 200,000 that a pope "must open his arms to protect all of God's people and embrace with tender affection the whole of humanity, especially the poorest, the weakest, the least important."
"I would like to ask all those who have positions of responsibility in economic, political and social life, and all men and women of goodwill: Let us be protectors of creation, protectors of God’s plan inscribed in nature, protectors of one another and of the environment."
Francis, an Argentine formerly known as Cardinal Jorge Mario Bergoglio, also spoke of humility, in keeping with expectations that he will take a more modest approach than predecessors.
"Let us never forget that authentic power is service. Only those who serve with love are able to protect."
According to CBC, the crowd interrupted the homily several times with applause, especially when he spoke about love and the need to protect the environment. He said:
"It means protecting people, showing loving concern for each and every person, especially children, the elderly, those in need, who are often the last we think about. It means caring for one another in our families: Husbands and wives first protect one another, and then, as parents, they care for their children, and children themselves, in time, protect their parents. It means building sincere friendships in which we protect one another in trust, respect, and goodness. In the end, everything has been entrusted to our protection, and all of us are responsible for it. Be protectors of God’s gifts!"
Attending the mass were representatives from 132 nations — including Vice-President Joe Biden, and the leaders of Christian, Jewish, Muslim, Buddhist and Janist faiths.
Rodrigo Grajales, a 31-year-old Colombian priest, told Agence France-Presse:
"With Pope Francis, the Church will be closer to the people and to the modern world."