Chaput said the theme was inspired by the words of an early church father, St. Irenaeus, who said, "The glory of God is man fully alive."
It reflects the central role of the family in teaching people how to give and receive love, officials said.
"In like manner, the glory of men and women is the capacity to love as God loves," Chaput said. "These words are also inspired by His Holiness Pope Francis, who embodies the message of mercy, joy, and love that lies at the heart of the Gospel."
Paglia said he wanted the gathering to be global in scope.
"I would like that this event would be an international event, an ecumenical event, and an interreligious event," Paglia said in halting English.
"I think it is really important that the next World Meeting of Families will be held in Philadelphia," Paglia said. "The city, the nation and the world would celebrate the importance of family . . . for all people."
Officials said the gathering, which is scheduled for Sept. 22 to 27, 2015, and is expected to draw more than one million people, will be viewed by millions around the world. The last World Meeting of Families was held in Milan, Italy, in 2012. Its theme was "The Family, Work, and Inspiration."
After introducing Corbett and Nutter, who in March accompanied Chaput to Rome to urge Francis to come to Philadelphia, the archbishop pointed out that the gathering "will bring diverse communities together - even Republicans and Democrats."
Corbett said the event "reflects the diversity of that world, and it reflects the diversity of religions also, and that is the beauty of this. I can't think of a better place than Philadelphia to do this in."
Nutter emphasized that the event would be good for Philadelphia.
"This is one more opportunity for everyone to experience Philadelphia. They will love it. They will live it. They will experience it," Nutter said. "Families will be strengthened as a result."
Before addressing reporters, Paglia, who arrived in Philadelphia on Monday night, spoke with about 20 college students from Waldorf College in Forest City, Iowa, who had been touring the city's historical area.
The students told Paglia they were choir members and that they were pleased to meet an envoy from the Vatican. The moment inspired a brief serenade.
Adam Luebke, choir director and a native of Doylestown, said the vocalists did an impromptu version of the hymn Ubi caritas.
"It was so awesome," said student Courtney Smith. "It was so much fun."
It would be the first touristy event in a day full of them for Paglia.
After the news conference ended, the delegation boarded a Phlash bus to visit the Cathedral Basilica of SS. Peter and Paul, Old St. Mary's Church, and the Philadelphia Museum of Art.
For the record, Paglia walked up the Rocky steps. And, after instructions from Chaput, he assumed the Rocky pose in front of the iconic statue.
Paglia's sightseeing will continue Wednesday: He is scheduled to visit Roman Catholic High School, the shrine of St. John Neumann and the Convention Center, before proceeding to New York and the United Nations.