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Pope Francis Celebrates Mass in Philadelphia With Local Priests, Nuns

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Ahead of Pope Francis' appearance Saturday at the Festival of Families, comedian Jim Gaffigan was prepping for his big gig -- opening for the pontiff.

Pope Francis conducted a mass in Philadelphia on Sept. 26, 2015. (Credit: CNN)

Pope Francis conducted a mass in Philadelphia on Sept. 26, 2015. (Credit: CNN)

Gaffigan, a devout Catholic, performs clean comedy and said "the pressure is on" for this show.

Asked how he landed the role, Gaffigan joked, "I think they searched throughout North America for the worst Catholic there is."

Gaffigan, whose five kids and wife will be in the audience, is one of several stars performing at the Festival of Families.

"It's going to be an adventure, but the energy feels electric here," he told CNN.

Gospel and soul great Aretha Franklin was expected sing a song or two and actor Mark Wahlberg, also a Catholic, will emcee the event.

With many streets closed, families were walking to the festival, hours before the Pope was due to arrive.

Francis will visit the festival after making an address on religious freedom and immigration at Independence Mall.

Philadelphia Archbishop Charles Chaput says he personally petitioned the Pope to speak about religious freedom during his visit to the city.

Francis obliged, but added another topic to his highly anticipated address: immigration.

It's an issue the Pope has mentioned on almost every stop during his six-day trip to the United States, often in extremely personal terms. He's repeatedly referred to himself as a "son of immigrants." On the Pope's helicopter ride to the airport in New York, Cardinal Timothy Dolan showed him Ellis Island, an important place for many immigrants.

Earlier Saturday, at a Mass before more than 2,000 mostly priests, women religious and deacons, Francis invoked the name of Katharine Drexel, who founded the Sisters of the Blessed Sacrament. He called her "one of the great saints raised up by this local Church."

Francis praised the "efforts of all those dedicated priests, religious and laity who for over two centuries have ministered to the spiritual needs of the poor, the immigrant, the sick and those in prison."

He spoke of "the hundreds of schools where religious brothers and sisters trained children to read and write, to love God and neighbor, and to contribute as good citizens to the life of American society."

A couple of nights earlier, Francis expressed his "esteem and gratitude to the women religious of the United States" at St. Patrick's Cathedral in New York.

"What would the Church be without you?" Francis said to applause.

The Mass at the Cathedral Basilica of Saints Peter and Paul was a spiritual boost for the city's clergy, who have been battered in recent years by sexual abuse scandals, parish mergers and school closings.