VATICAN CITY -- Pope Benedict XVI, accepting the Ring of the Fisherman and the woolen mantle that symbolize his authority, yesterday declared the extraordinary outpouring of grief over the death of his predecessor to be evidence of the Roman Catholic Church's vitality and urged young people to embrace Christian faith.
Presiding at a festive inauguration Mass in St. Peter's Square, where just 16 days earlier he had led millions of mourners in a somber funeral Mass for Pope John Paul II, Benedict offered a plea for unity in his divided church and reached out to other Christians, to Jews, and to ''nonbelievers."
''How alone we all felt after the passing of John Paul II -- the pope who for over 26 years had been our shepherd and guide on our journey through life," said Benedict, wearing a golden chasuble and a golden miter and sitting in a white throne atop a stepped platform. ''And now, at this moment, weak servant of God that I am, I must assume this enormous task, which truly exceeds all human capacity. How can I do this? How will I be able to do it? . . . All the saints of God are there to protect me, to sustain me, and to carry me. And your prayers, my dear friends, your indulgence, your love, your faith, and your hope accompany me."
The Mass was a model of outreach and humility by a new pope who until last week was thought of as a rigid hardliner in his role as prefect of the Vatican's Congregation for the Doctrine of the Faith. Benedict, 78, smiled and waved during the Mass, and, at the end of the liturgy, which lasted two hours and 40 minutes, he stepped onto an open-air white jeep, with two Vatican flags on the hood, and rode through the cheering crowd making gestures of blessing.
''Yes, the Church is alive -- this is the wonderful experience of these days," he said. ''During those sad days of the pope's illness and death, it became wonderfully evident to us that the Church is alive. And the Church is young. She holds within herself the future of the world and therefore shows each of us the way toward the future."
His 35-minute homily, primarily a theological explanation of the symbolism of the ring and the mantle, called a pallium, was interrupted three dozen times by applause. Periodically, during the Mass, sections of the crowd chanted ''Benedetto," his name in Italian, or simply, ''Papa!"
''It was very clear, from when he began the Mass with his wave and people could see that on the Jumbotrons, that there was a nice responsive acclamation from the crowd," the president of the US Conference of Catholic Bishops, Bishop William S. Skylstad of Spokane, said in an interview. ''Certainly he is very different than John Paul II, but his smiling and his attempt to reach out -- people love to sense a warmness of heart and a sense of hospitality. He just did very well, and his voice was strong."
The Mass, in Latin with a homily in Italian, featured readings in English and Spanish, the Gospel in both Latin and Greek, and prayers in Arabic, Chinese, French, German, and Portuguese. Three narrators offered periodic explanations of the significance of the ritual, in German, English, and Italian, to the crowd via loudspeaker. And Benedict gave Communion to dozens of people from around the world.
In a break from tradition, Benedict did not require all 150 cardinals present to kneel before him to signal their obedience -- an act they have already performed twice since his election on Tuesday. Instead he chose a group of 12 Catholics -- three cardinals, a bishop, a priest, a deacon, a nun, a brother, a married couple, and two recently confirmed young people -- to kiss his new ring and swear obedience as symbolic representatives of the whole church.
''I find myself really impressed by him," said Maria Magdalena Miriami, 51, of Rome, who attended the Mass. ''Now he seems to have charisma, where as before I found him really shy. I feel closer to him more than I did three years ago."
And Sister Eva Janning of Toronto said, ''I was at first a little taken aback by the choice, but I am very happy about it now, because of the reaction I hear from everywhere. Critics see him in the role of his last ministry, but now his role is also to be the papa, the father of the church."
Others never had any doubt. Two students in Rome, Anthony Valle, 33, from Queens, and his wife, Marta Valle, 30, of Essen, Germany, attended the Mass holding a photograph showing the couple being married last year by Benedict, whom they asked to preside when they showed up at a Mass he was celebrating. ''We're not nobility or aristocracy or movie stars, but he said 'yes,' " Anthony Valle said. ''He's such a great man -- so humble, so pastoral -- and he very much works person to person."
The inauguration -- a ceremony called a coronation until John Paul I abandoned the practice of wearing a tiara -- was attended by a crowd estimated by the Vatican at 500,000 people, who packed into St. Peter's Square and spilled onto Via della Conciliazione and the surrounding streets. Many in the crowd waved national flags from all over the world, including a large number from Germany, Benedict's native country. The Polish flags that were omnipresent during the pontificate of John Paul II were hardly visible at all yesterday, but in the front section, a group unfurled a banner reading ''Wadowice," the name of the late pope's hometown.
Amid the enthusiasm, some people said they hope Benedict will prove to be more of a reformer than his history as the Vatican's top enforcer of doctrinal orthodoxy might suggest.
''The church has to find a more modern way," said Edith Pforringer, a Bavarian tour organizer who led to the Mass a group of 240 people from the region where Benedict, born Joseph Ratzinger, lived.
On the large stage in front of St. Peter's Basilica sat, to the right of the altar, 141 governmental delegations, including King Juan Carlos and Queen Sofia of Spain, King Carl XVI of Sweden and, representing the United States, Governor Jeb Bush of Florida, President Bush's brother and a convert to Catholicism. To the left of the altar sat hundreds of bishops and priests and 70 non-Catholic religious leaders, including the Archbishop of Canterbury, Rowan Williams; the chief rabbi of Rome declined an invitation because yesterday was the first day of Passover.
''With great affection I also greet all those who have been reborn in the Sacrament of Baptism but are not yet in full communion with us; and you, my brothers and sisters of the Jewish people, to whom we are joined by a great shared spiritual heritage, one rooted in God's irrevocable promises," Benedict said, alluding to the church's theological position, arrived at after the Holocaust, that the covenant between God and the Jewish people was not superceded by the advent of Christianity. ''Finally, like a wave gathering force, my thoughts go out to all men and women of today, to believers and nonbelievers alike."
The heart of the ceremony, and of Benedict's homily, was the new pope's reception of the Ring of the Fisherman and the pallium.
Before the Mass began, Benedict went to what Catholics believe is the tomb of the apostle Peter, below the papal altar in St. Peter's Basilica, to pray. He perfumed the tomb with incense, and processed from the tomb to the outdoor altar.
During the liturgy, Cardinal Jorge Arturo Medina Estevez of Chile placed the pallium on the pope, and Cardinal Angelo Sodano of Italy placed the ring on the pope's right hand.
Benedict chose to adopt an ancient form of the pallium, a white mantle made of lamb's wool and embroidered with five red crosses, that is longer than those worn by recent popes. The pallium is intended to be a reminder of Jesus placing a lost sheep on his shoulders; the red crosses are evocative of Jesus' blood, and three are pierced with pins to represent the nails of crucifixion.
The Ring of the Fisherman has an image of St. Peter, regarded as the first pope, with a boat and a net, a reminder of an incident in the Gospel in which Peter enjoys a miraculous catch of fish after he puts his faith in Jesus.
Today Benedict is scheduled to meet with German pilgrims, and then to visit the tomb of the apostle Paul at the basilica of St. Paul's Outside-the-Walls in Rome. In an effort to visit all four patriarchal basilicas, including St. Peter's and St. Paul's, Benedict plans on May 7 to visit St. John Lateran, the cathedral of the Rome diocese, and then later to visit the Basilica of St. Mary Major, which is headed by Cardinal Bernard F. Law, the former archbishop of Boston.
Globe correspondent Sofia Celeste contributed to this report. Michael Paulson can be reached at firstname.lastname@example.org.