Faithful attend Pope Benedict XVI's last Angelus prayer, in St. Peter's Square, at the Vatican, Sunday, Feb. 24, 2013. Benedict XVI gave his pontificate's final Sunday blessing from his studio window to the cheers of tens of thousands of people packing St. Peter's Square, but sought to reassure the faithful that he wasn't abandoning the church by retiring to spend his final years in prayer. The 85-year-old Benedict is stepping down on Thursday evening, the first pope to do so in 600 years, after saying he no longer has the mental or physical strength to vigorously lead the world's 1.2 billion Catholics. (AP Photo/Riccardo De Luca)
VATICAN CITY (AP) — With a humble "Grazie" as bishops doffed their mitres and applause echoed through St. Peter's Basilica, a frail Pope Benedict XVI began his long farewell by presiding over Ash Wednesday services in a tearful, final public Mass.
"We wouldn't be sincere, Your Holiness, if we didn't tell you that there's a veil of sadness on our hearts this evening," said Cardinal Tarcisio Bertone, Benedict's longtime deputy, his voice breaking.
"Thank you for having given us the luminous example of the simple and humble worker in the vineyard of the Lord," Bertone said, quoting Benedict's own words when he first appeared before the faithful above St. Peter's Square after he was elected pope.
Smiling and clearly moved, Benedict responded, "Grazie. Now let us return to prayer" — his words bringing to an end the resounding applause that had grown in intensity over several minutes.
Then, in a rare gesture and sign of respect, the rows of bishops, some with tears in their eyes, removed their mitres. One prelate dabbed at his eyes with a handkerchief.
"Viva il papa!" someone in the crowd shouted as the pope slowly made his way down the steps of the altar, assisted by two clergymen. He then departed St. Peter's for the last time aboard a wheeled platform, sparing him the long walk down the aisle.
Ash Wednesday marks the start of Lent, the most solemn season on the church's liturgical calendar that ends with Holy Week, when the faithful commemorate the death of Christ and his resurrection on Easter Sunday. By this Easter, on March 31, the church will likely have a new pope.
In his final homily as pontiff, Benedict sent a clear message to his successor and those who will elect him of his hope for the future: a united church that isn't "defiled" by internal rivalries.
Each Christian, he said, is called to bear witness to the faith. "I think in particular of the attacks against the unity of the church, to the divisions in the ecclesial body," he said.
"Experiencing Lent in a more intense and evident ecclesial union, moving beyond individualisms and rivalries, is a humble and precious sign for those who have drifted from the faith or are indifferent to it."
Earlier in the day, the scene was festive as Benedict took the extraordinary step of speaking directly to the faithful about why he had broken with 600 years of tradition and decided to retire on Feb. 28.
"As you know, I have decided to renounce the ministry that the Lord gave to me on April 19, 2005," Benedict told thousands gathered for the traditional Wednesday general audience. "I did this in full liberty for the good of the church."
He expressed gratitude for the prayers and love of his flock, which he said he "physically felt in these days that haven't been easy for me." And he asked them to "continue to pray for me, the church, and the future pope."
Benedict was greeted with a standing ovation when he entered the packed hall, and his speech was interrupted repeatedly by applause.
A huge banner reading "Grazie Santita" — "Thank you Your Holiness" — was strung up and a chorus of Italian schoolchildren serenaded him with one of his favorite hymns in German — a gesture that moved the pope to thank them for singing a piece "particularly dear to me."
He appeared wan and spoke softly, but his eyes twinkled at the welcome.
"He gave us eight wonderful years of his words," said Ileana Sviben, an Italian from the northern city of Trieste. "He was a wonderful theologian and pastor."
The Rev. Reinaldo Braga Jr., a Brazilian priest studying theology in Rome, said he was saddened when he first heard the news of Benedict's retirement.
"The atmosphere was funereal," he said. "But then I realized it was a wise act for the entire church. He taught the church and the world that the papacy is not about power, but about service."
It was a sentiment Benedict himself emphasized Wednesday, saying the "path of power is not the road of God."
Benedict's decision has placed the Vatican in uncharted waters: No one knows what he'll be called or even what he'll wear after Feb. 28.
The Vatican revealed some details of that final day, saying Benedict would attend a morning farewell ceremony with his cardinals and then fly by helicopter at 5 p.m. to the papal summer retreat at Castel Gandolfo.
That means he will be far from the Vatican when he ceases being pope at 8 p.m. — a deadline Benedict himself chose because that's when his normal workday ends.
Vatican spokesman the Rev. Federico Lombardi said no formal or symbolic act was needed to make the resignation official, because Benedict has already done all that was required by affirming publicly he had taken the decision freely.
Benedict's final official acts as pope will include audiences with the Romanian and Guatemalan presidents this week and the Italian president on Feb. 23. His final general audience is Feb. 27.
To assure the transition goes smoothly, Benedict made an important appointment Wednesday, naming the No. 2 administrator of the Vatican city state, Monsignor Giuseppe Sciacca, as a legal adviser to the camerlengo.
The camerlengo, or chamberlain, helps administer the Vatican bureaucracy in the period between Benedict's resignation and the election of a new pope. The current camerlengo is Bertone, the Vatican secretary of state.
He and Cardinal Angelo Sodano, the dean of the College of Cardinals, will have a major role in organizing the conclave, during which the 117 cardinals under the age of 80 will vote on who should succeed Benedict.
The Vatican has made clear that Benedict will play no role in the election of his successor, and once retired, he will live a life of prayer in a converted monastery on the edge of the Vatican gardens.
But his continued presence within the Vatican walls has raised questions about how removed he really will be from the life and governance of the church. Lombardi acknowledged that Benedict would still be able to see friends and colleagues.
"I think the successor and also the cardinals will be very happy to have very nearby a person that best of all can understand what the spiritual needs of the church are," Lombardi said.
Still, Benedict is expected to keep a low public profile.
As a result, his last appearances as pontiff are expected to draw large crowds for what may well be some of the last speeches by a man who has spent his life — as a priest, a cardinal and a pope — teaching and preaching.
And they will also give the faithful a way to say farewell under happier circumstances than when his predecessor, Pope John Paul II, died in 2005.
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Associated Press staffers Trisha Thomas and Daniela Petroff in Vatican City contributed to this report.