But, he said, "no bishop will give more joyfully of himself than I will to renewing this great church. No bishop will try harder to help persons who have been hurt by the sins of the past. And no bishop will work harder to strengthen and encourage our priests and restore the hearts of our faithful."
Chaput, 66, succeeds Cardinal Justin Rigali, who is retiring after eight years at the helm of the 1.5 million-member archdiocese.
A half-dozen cardinals, about 200 bishops, and 400 priests in cream-and-gold vestments preceded Chaput to the main altar of the cathedral. Rigali followed, carrying an ornate crosier, or bishop's staff, of brass and silver.
In his final gesture as archbishop, Rigali first took his seat in the large oak-and-velvet bishop's chair. Chaput sat in a smaller chair opposite him.
After a representative of the papal nuncio's office read Pope Benedict XVI's July 19 edict naming Chaput to Philadelphia, Rigali rose, crossed the altar, and escorted the former Denver archbishop to the chair in the formal act of succession.
At that, the congregation rose and applauded Chaput for more than 90 seconds.
Later, the Kansas-born Franciscan Capuchin friar took hold of the plain wooden shepherd's staff that he had brought with him from Colorado as the symbol of his new office.
In his homily, he remarked that a friend had recently told him the elaborate preparations for his installation reminded him of "a very, very, very big wedding," which elicited some chuckles.
"Of course, my appointment to Philadelphia is an arranged marriage," he said to even more laughter.
The analogy was apt, he said, because "the relationship of a bishop and his church is very close" to that of an arranged marriage, where two parties must learn to live harmoniously after they are united.
In his 14 years as archbishop of Denver, Chaput earned a national reputation as a leader who forcefully exhorted his flock to live and vote their Catholic faith. At his installation here, he invoked St. Augustine's description of the role of a bishop:
"To take the part of the weak, to refute opponents . . . to shake the indolent awake . . . help the poor, liberate the oppressed, encourage the good, suffer the evil, and love all men."
Though the mood inside the ornate cathedral was welcoming, a few of Chaput's doubters and critics stood outside holding signs.
"He's out of the Middle Ages," said the Rev. Robert Hoatson, a priest of the Archdiocese of Newark, N.J., and an advocate for victims of clergy sex abuse. "He's a charmer, and he comes off as very collaborative and inclusive. But he's very hierarchical."
In February, the Philadelphia District Attorney's Office arrested two priests, a defrocked priest, and a parochial-school teacher accused of raping two boys in the 1990s, and charged the former head of the archdiocesan clergy office with child endangerment.
Also that month, a Philadelphia grand jury found that as many as 37 archdiocesan priests accused of inappropriate behavior with minors were still serving in ministry. Rigali later placed 27 priests on administrative leave pending an archdiocesan investigation.
"The church is not defined by her failures," Chaput told the congregation Thursday. "What we do in the coming months and years to respond to these challenges, that will define who we really are."
Among the dozens of dignitaries and laypeople presented to Chaput at the altar was District Attorney Seth Williams, whose office wrote the grand jury report and ordered the arrests. He was followed by Mayor Nutter.
In his closing remarks, Chaput thanked Rigali for his "years of leadership to the church in Philadelphia . . . and the Catholic community worldwide." The congregation rose and applauded for nearly a minute.
Rigali, who now will make his home in the Diocese of Knoxville, Tenn., will continue to serve on the Vatican's Congregation for Bishops. Before coming to Philadelphia in 2003, he was archbishop of St. Louis, and he had previously served 34 years in the Vatican's diplomatic office.
During the recessional at the close of the Mass, Chaput stopped to shake so many hands - plunging into the pews to greet former U.S. Sen. Rick Santorum, among others - that he was left standing alone in the center aisle as the others passed through the main door about 50 yards away.
He later greeted hundreds of well-wishers in the vestibule.
"He seems like a very simple man, very genuine," said Maryanne Fasco of SS. Peter and Paul Parish in West Chester. She and her family were among those who greeted Chaput during the service.
Ed Scott, 59, of Our Lady of Sorrows parish in West Philadelphia, described Chaput as "very down to earth," and expressed the hope that "he brings refreshing change."
Contact staff writer David O'Reilly at 215-854-5723 or email@example.com.
Inquirer staff writer John P. Martin contributed to this article.