Pope Francis arrived in Philadelphia today, where his last two days in the United States will be spent visiting ordinary Catholics and promoting the issue of religious freedom.
The pontiff celebrated Mass in the city at the Cathedral Basilica of Saints Peter and Paul, the largest brownstone structure in Philadelphia and the largest Catholic church in Pennsylvania.
In a homily, Francis challenged young Catholics to service.
"One of the great challenges facing the Church in this generation is to foster in all the faithful a sense of personal responsibility for the Church's mission, and to enable them to fulfill that responsibility as missionary disciples, as a leaven of the Gospel in our world," he said.
"This will require creativity in adapting to changed situations, carrying forward the legacy of the past not primarily by maintaining our structures and institutions, which have served us well, but above all by being open to the possibilities which the Spirit opens up to us and communicating the joy of the Gospel, daily and in every season of our life," the pope said.
Later, Francis is scheduled to visit St. Charles Borromeo Seminary and Independence Hall, where he will deliver a speech.
Later, he will be the featured guest at the World Meeting of Families conference with some 18,000 attendees.
On Sunday, his last day on U.S. soil, he will celebrate outdoor Mass, expected to draw 1.5 million people.
NPR's Jeff Brady spoke with a souvenir seller outside the Philadelphia Convention Center who was happy for the surge in business but not by the tight security measures.
"They shut down the whole city — they shut down the bridges, the buses --for one person! That's crazy! They don't do this for the President!," Christian Andrews-Fulton said.
As The Associated Press reports, the pope "will give his attention to both the elite and the disadvantaged, this time visiting inmates in Philadelphia's largest jail. On Saturday night, he will be serenaded by Aretha Franklin and others on the Benjamin Franklin Parkway at a festival celebrating families. He will return there Sunday for the Mass, his last major event before leaving for Rome."
The trip to Philadelphia follows the pope's travels to Washington, D.C. and New York. In the nation's capital, he addressed a joint meeting of Congress, urging law makers to cooperate to solve problems such as inequality of opportunity and climate change – themes that he echoed and expanded on at the United Nations General Assembly in New York.