Secrecy under penalty of excommunication also ensures that the winner doesn't know who among his cardinals voted against him — an important element going forward to keep the church's top leadership unified.
"It's not the Renaissance where he'd be poisoned, but it's a matter of human respect," Wister said.
Once the final oath is taken, the master of liturgical ceremonies gives the order "Extra omnes" (everyone out) and all those not taking part in the conclave leave the frescoed walls of the chapel.
An elderly cardinal, over age 80 and thus ineligible to participate, remains and reads a meditation about the qualities a pope should have and the challenges facing the church, after which he and the master of ceremonies leave the cardinals to begin voting.
On Day 1, only one round of balloting is taken; after that cardinals cast two votes in the morning, two in the afternoon until they have a victor. A two-thirds majority is necessary.
Each cardinal writes his choice on a paper inscribed with the words "Eligo in summen pontificem," or "I elect as Supreme Pontiff." They approach the altar one by one and say: "I call as my witness, Christ the Lord who will be my judge, that my vote is given to the one who, before God, I think should be elected."
The folded ballot is placed on a round plate and slid into an oval urn. After the votes are counted and the outcomes announced, the papers are bound together with a needle and thread, each ballot pierced through the word "Eligo." Then they are burned with a chemical to send black smoke (meaning no) or white (meaning yes) out of the Sistine Chapel's chimney.
On April 19, 2005, a stunned Ratzinger accepted the charge and was brought into a side room to change into the white vestments of the papacy. Off came the scarlet cassock; underneath was the simpler black clerical garb of a cardinal.
"Naturally the pope couldn't change completely at that moment, so he went out with those black sleeves — we could see his sweater!" Marini recalled. "But even that was a human gesture of how he was dressed as a cardinal."
Marini accompanied Ratzinger out onto the loggia of the basilica overlooking St. Peter's Square where a cardinal announced "Habemus Papam" (We have a pope) to the thousands of people below. The cardinal announced Ratzinger's name in Latin, and then Benedict uttered his first public words as pope, saying he was but a "simple, humble worker in the vineyard of the Lord."
Marini noted that that first encounter of the new pope with his flock traces its history to the ancient tradition that the bishop of Rome is elected by the people.
"This appearance by the pope on the balcony, the applause and cheers of joy that erupt when he comes out," he said, "in some way represents the Roman people accepting their pope."
It's one of the potent symbols of a tradition-drenched conclave.
"A religion relies on its customs and practices," said Monsignor Kevin Irwin, former dean of theology at Catholic University of America and professor of liturgy. "This is not like putting up posters and getting a poll of who is winning. This is an act of God."
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