"I think this homily shows he realizes he's not going to be elected. He's too much of a polarizing figure," McBrien said. "If he were elected, thousands upon thousands of Catholics in Europe and the United States would roll their eyes and retreat to the margins of the church."
A potential rival to Ratzinger is another influential cardinal, Carlo Maria Martini, the retired archbishop of Milan, whose philosophy sometimes clashes with Ratzinger's. Because of health problems, Martini is not regarded as a prime papal candidate, but he is a standard-bearer for change in the church.
Black smoke rises from the chimney above the Sistine Chapel, indicating that the first vote by the cardinals had failed to elect a new pope.
A year ago in an interview with the Rome newspaper Il Tempo, he called for power-sharing with bishops -- so that they become "a council of regents for the church, besides the pope" -- and for discussion of the ordination of women, priestly celibacy and other controversial topics.
Historically, senior cardinals who were respected enough to be mentioned as candidates exerted strong influence at conclaves. Both Martini and Ratzinger are 78.
After Monday's Mass, the cardinals filed out of the basilica for lunch at their residence within the Vatican walls. At 4:30 p.m., they began a slow procession from the Apostolic Palace, the huge Renaissance structure of frescoed galleries, apartments and meeting rooms, to the Sistine Chapel.
After the river of red caps and robes flowed through the chapel door, the cardinals stood behind long tables set up specially for the vote. Each then swore an oath of secrecy at a podium set under Michelangelo's giant fresco of Jesus presiding over the Last Judgment; among other images, the fresco portrays evil-doers on their way to hell.
Ratzinger, as dean, was first to take the oath, which pledges "secrecy regarding everything that in any way relates to the election of the Roman pontiff." He then placed his hand on an open copy of the Gospels to seal the promise.
After all the cardinals had made the same pledge, Vatican television cameras were turned off and the doors of the chapel were closed. Although the televised images were unprecedented, the broadcast fell into line with the broad media access provided for the several past days of transition ceremonies.
Reporters' contact with the cardinals, however, was sharply proscribed shortly after John Paul's April 8 funeral. In refusing to speak to journalists, the cardinals ended a tradition of open pre-conclave discussion of church issues.
Secrecy within the Sistine Chapel is safeguarded by new high-tech measures. A false floor was installed last week to accommodate electronic anti-bugging devices, Vatican officials said. Mobile phones, radios, television sets and Internet connections all are prohibited at the cardinals' temporary Vatican residence to ensure no information leaks into or out of the conclave.