PHILADELPHIA – It was a once-in-a-lifetime opportunity to attend the World Meeting of Families – and a road trip Justin Alvarez, his wife and their eight kids between the ages of 2 and 14 always had wanted to make.

Plus, Alvarez, who heads the Ventura, Calif., chapter of the Catholic Association of Latino Leaders, had been following the story of another family driving to the event from Argentina. That made their “road trip feel very small indeed.”

That’s how he and his family ended up spending the last week driving an RV cross-country from Thousand Oaks, Calif., to the World Meeting of Families in Philadelphia, stopping to see family and friends and visit Catholic colleges along the way.

“It was an adventure, yes. It was fun most of the time,” he laughed.

More than 17,500 pilgrims, like the Alvarez family, from more than 100 countries are registered to attend the weeklong event hosted by the Holy See’s Pontifical Council for the Family and the Archdiocese of Philadelphia, according to Archbishop Charles J. Chaput of the Archdiocese of Philadelphia.

That makes the eighth World Meeting of Families that kicked off Tuesday afternoon just before Pope Francis arrived in the United States the largest in history, Chaput said.

By comparison, about 7,000 people registered for the last World Meeting of Families, held in 2012 in Milan, Donna Crilley Farrell, executive director of the World Meeting of Families, has said.

“All have come to affirm their commitment to the family as the foundation of a fruitful life – the place where we first learn to love and to share and to be agents of justice in the world,” Chaput said.

In addition to the Alvarez family, that included Sindisiwe Blandina, who traveled to Philadelphia with a group of more than 20 people from her church in Harare, Zimbabwe. Wearing a dress printed with the colorful World Meeting of Families logo and Philadelphia LOVE statue, she said, she’d come all that way because she wanted to see the pope.

A ‘historic’ event

This is the first time the World Meeting of Families, held every three years, has been hosted in the United States and the first time it has been hosted in a country that is not majority Catholic. That’s “really meaningful” because of the role the U.S. plays on the international stage, said Archbishop Vincenzo Paglia, president of the Pontifical Council for the Family.

Philadelphia Mayor Michael Nutter called it “the most historic event in modern Philadelphia history.”

It also is the “central reason” Francis has said he is visiting the United States ¬– the largest of the public events he will take part in during his visit, Chaput said. A million people are estimated to flood Benjamin Franklin Parkway by the end of the week for the event’s closing Mass celebrated by the pope.

And it comes just a month before the Synod of Bishops on the family. Paglia said the discussions at the World Meeting of Families will have a “great effect” on the synod, while Chaput declined to speculate, noting he’d been “focused on something else.”

The archdiocese has been planning the event since June 2012, according to Farrell. The pope confirmed his attendance in last November.

‘Love is our mission’

Barron admitted during his keynote he still was getting used to his new outfit as the newly ordained auxiliary bishop of Los Angeles — the black cassock with colored trim and the zucchetto that always feels like it’s falling off his head. Previously, he had been rector and president of the University of Saint Mary of the Lake/Mundelein Seminary outside Chicago.

He spoke about living as the imago dei, made in the image of God – a call that echoed the World Meeting of Families’ theme, “Love is our Mission: The Family Fully Alive.”

“The imago dei is not some little special private thing we hang on to for our own spiritual benefit. Rather … the image of God is for the world. We must think of ourselves as representatives of God, bringing His power, His wisdom, His mind to the world,” he said.

“The image of God is a mission and a responsibility.”

Along the way, Barron explained the law in terms of golf in the characteristic style that has made him the most-followed Catholic leader on social media after the pope, according to his ministry, Word on Fire. He wasn’t very good at the game until a coach corrected his swing – until he gave him laws that disciplined his mind and body so he could do what he always wanted to do, he said.

The law is not the enemy of freedom, he said, but “the condition for the possibility of freedom.”

Other sessions scheduled during the World Meeting of Families include titles such as “The Special Place of Women in the Family, the Church, and the World,” “Caring for Creation: Pope Francis and Environmental Stewardship,” “The Hispanic Family in the Context of a Multicultural Society” and “‘Always Consider the Person’: Homosexuality in the Family.”