"My favorite part is when we bring these guest artists into this room and they look out at 21,000 seats and say, 'You're going to fit how many people in here?!"' said Barry Anderson, who handles logistics for the choir. "And we just say, 'Oh, yeah. We'll fill it up, all four shows.' "

Rehearsals and performances — held on about 140 days a year — mean a typical member can easily spend 15 hours a week in choir-related activities. Come late November, the commitment becomes virtually a second job, up to six days a week. Tours, often overseas, can mean setting aside two to three weeks' vacation every other year.

Most members work day jobs, and a random sampling turns up public school teachers, doctors, secretaries, postal workers and salesmen. A common faith keeps them coming back, with the average member singing about 13 years with the choir.

"If they can't keep the commitment, they don't last very long," said Robb Cundick, a choir member for 16 years, who chronicles the choir's concerts and travels.

Members must be Mormons in good standing with the church, between 25 and 55 and nominated by their local bishop before they can try out. They are asked to assess their relationship with God, their family, within their professions and as volunteers. They also must live within 100 miles of Salt Lake's Temple Square, and many commute at least an hour each way.

The sacrifice, they say, is a small price to be part of a tradition dating to 1847, when Brigham Young brought a band of Mormon pioneers to the shores of the Great Salt Lake to escape religious persecution. Its first formal performance came just 29 days after the Mormons arrived.

Jessop estimates that two-thirds of current-day choir members can trace their roots to the Mormon pioneers.

This year, passes for the Christmas concerts, which are free, went faster than tickets to a recent Rolling Stones concert just down the street. Fans lined up overnight to be the first in line, and the choir's Web site locked up soon after orders started being accepted. Within an hour, every seat for each concert was taken.

Acclaimed soprano Renee Fleming will perform with the choir, with British actress Claire Bloom narrating the program. In recent years, the choir has appeared with other mainstream figures, including Sting, Walter Cronkite and Angela Lansbury.

On Christmas morning, the choir will give one of its weekly Sunday concerts, and that, said Gehris, is the big payoff. Just as the world and their fellow Mormons will be watching them, choir members will be looking out into the concert hall, looking for signs that their singing is making a spiritual connection for Christmas.