SALT LAKE CITY — There's just one thing that could ruin David Gehris' Christmas season: Being singled out on stage as a member of the renowned Mormon Tabernacle Choir.

If he is, Gehris will know he messed up, big time.

In front of a live audience of 21,000 in the ornate LDS concert hall. In front of millions more listening in 2 dozen countries. Worse, in front of the assembled faithful here in the seat of The Church of Jesus Christ of Latter-day Saints.

"You never want to be singled out," said Gehris, who has sung bass with the choir for 20 years.

Better to leave the soloing to the guest singer and avoid a flash of disapproval from the director.

For the all-volunteer, all-Mormon choir, the reward in performing the famous Christmas concerts this week comes in being a small, self-sacrificing part of 360 voices that are only famous in harmony. When they hit it right — and their Emmy and Grammy awards and platinum records suggest they often do — they say the experience isn't next to godliness, it is godliness itself.

Singing, choir members say, is their spiritual mission to the church.

No other performances are as important, joyous — or potentially stressful — than the four Christmas concerts, which began Thursday. Four concerts that filled up 84,000 available seats in less than one hour.

"It's a tremendous honor that requires tremendous commitment and sacrifice," said Craig Jessop, choir director since 1999.

In a typical year, more than 300 singers, many with years of formal training, will try out for a coveted choir spot. Only 10 percent will make the cut, after a grueling selection process that takes up to 15 months. About 30 percent of choir members failed their first auditions.

Once they're in, even routine practice sessions can be daunting to newcomers.

Rehearsals are held in the church's cavernous conference center, one of the world's largest religious concert halls. To the choir's front is the 110-member Orchestra at Temple Square, its instrumental counterpart. Behind is a massive 7,708-pipe organ, its deep tones resonating from the pipes of the organ built by the Schoenstein & Co. in San Francisco. On either side are towering Christmas trees and decorations, stretching nearly 100 feet to the ceiling.

"Anyone who comes in here is intimidated. If they say they're not, they're not being truthful," said Gehris, whose wife, Debra, also joined the choir 20 years ago.

Even professional guest artists pause and gape when they take the stage for the first time.

"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.' "