VATICAN CITY (AP) - Beginning a long farewell to his flock, a weary Pope Benedict XVI celebrated his final public Mass as pontiff, presiding over Ash Wednesday services hours after a bittersweet audience that produced the extraordinary scene of the leader of the world's billion Catholics explaining himself directly to the faithful.
The mood inside St. Peter's Basilica was somber during the Mass, as if the weight of Benedict's decision and the finality of his pontificate had finally registered with the thousands present. The basilica erupted in a rousing standing ovation as Benedict exited for the last time as pope, bringing tears to the eyes of some of those closest to him.
"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," Cardinal Tarcisio Bertone, Benedict's longtime deputy, told the pope at the end of the service, 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 words when he first appeared on the loggia overlooking 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 several minutes of thundering applause. Then, in a rare gesture and sign of respect, the bishops removed their mitres.
"Viva il papa!" the crowd yelled as the pope stepped off the altar, assisted by two clergymen, and departed St. Peter's aboard a moving platform to spare 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, which commemorates the death of Christ and his resurrection on Easter Sunday. By this Easter, on March 31, the church will likely have a new pope.
The scene was festive earlier in the day, when Benedict took the extraordinary step of speaking directly to his flock 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 said, to warm applause. "I did this in full liberty for the good of the church."
He thanked the faithful for their prayers and love, which he said he had "physically felt in these days that haven't been easy for me." And he asked them to "to continue to pray for me, the church, and the future pope."
Benedict looked tired but serene as he basked in a standing ovation when he entered the packed hall for his traditional Wednesday catechism lesson. His speech was interrupted repeatedly by applause, and many in the audience of thousands had tears in their eyes.
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 won over the pope, who thanked 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, too, was saddened when he first heard the news.
"The atmosphere was funereal but nobody had died," 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 the retiring 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 Benedict will be far from the Vatican when he ceases being pope at 8 p.m. - a deadline decided by the pope himself because that's when his normal workday ends.
Vatican spokesman the Rev. Federico Lombardi said no formal or symbolic act was needed to make his resignation official, because Benedict has already done all that was required to resign by affirming publicly he had taken the decision freely.