Pope Celebrates Last Public Mass as Pontiff Starting his public 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 pope explaining his decision to step down 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 of faithful present. But the basilica erupted in a rousing, minutes-long standing ovation as Benedict exited for the last time as pope, bringing tears to the eyes of some of his closest collaborators. "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 own words when he first appeared on the loggia overlooking St. Peter's Square after he was elected pope. "Viva il papa!" the crowd yelled as Benedict stepped off the altar. 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. 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. Benedict looked tired but serene as he basked in a standing ovation when he entered the packed hall for his traditional Wednesday catechism lesson. A huge banner reading "Grazie Santita" (Thank you Your Holiness) was strung up at the back of the room 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 very softly, but his eyes twinkled at the flock's welcome - warm and heartfelt if somewhat bittersweet. The Rev. Reinaldo Braga Jr., a Brazilian priest studying theology in Rome, said he, too, was saddened when he first heard the news.