BETHLEHEM - The Bethlehem Bach Festival looms in the classical music world much as the Statue of Liberty does: It'll always be there, and you're sure to visit at some point. Well, maybe. The now-or-never draw of its 100th season, however, is enough to make you gas up the car for its signature piece, Bach's

Mass in B minor

, a work widely considered unperformable until the amateur choristers of this heavily Moravian industrial town proved otherwise.

While the steel mills loom massive and quiet on the riverfront, Bach prevails in the two-week festival, through Saturday, with nods to innovation (the Paul Taylor Dancers perform) yet buttressed by curious, arcane traditions.

The Packer Memorial Church sits on the nicely gardened Lehigh University grounds, where musicians and audience picnic during the one-hour intermission. Inside the 860-seat church - mostly wood, low-ish ceiling, spartan, no cherubs - numerous listeners pulled out well-thumbed scores of the Mass. One lent me hers; it had handwritten notes about Bach's use of Mixolydian modes.

Everyone knows not to applaud until artistic director Greg Funfgeld, in residence since 1983, leaves the podium. (The resulting silence after the Mass quivered like no other.) Concerts are called "sessions." The program book's translation is credited to the local Episcopalian bishop. In the St. Matthew Passion, the audience is invited to sing with the chorales. Each soloist is paid through a specific evergreen fund: William Sharp sings the role of Christ in the Matthew Passion courtesy of "The L. Steven Porter Endowed Jesus Chair."

Contrary to trends of recent decades, this is big-chorus Bach. Once 300 voices, the Bach Choir is 100 but swelled to 150 for Saturday's Mass in B minor with a visiting, 75-year-old splinter group, Baldwin-Wallace College Choir. Lapses in concentration happened in the less-challenging passages. But spots so intricate that they're often reassigned to soloists - the "Et iterum venturus" in the Credo, for one - were managed by the chorus with spectacular unanimity.

With long-cultivated wisdom, Funfgeld discreetly accented key gestures in any given fugal strand so nothing important was lost in the mass of rich, well-molded choral sound. Phrasing was often identical to that of the Bach Choir's 1988 recording; so were some soloists, such as soprano Rosa Lamoreaux.

Tradition? Habit? Some practices warrant rethinking. Though the Mass was one of the better performances I've heard, the same soloists sing from one day to the next, and some, like the superb countertenor Daniel Taylor, sounded weary. After the long intermission, the chorus needed a while to regain its footing.

But then, each "session" isn't an end in itself, but a chapter in the festival's singular immersion experience. And if that chapter was more solid than compelling, it's as if the music's greatness is a given, proving that too blatantly could be in bad taste, or could get in the way of the inner experience Bach sought to produce. This is Bach performed with minimum ego, enacted by servants, not cocreators. That's a different ballgame - and worth traveling for.

Contact music critic David Patrick Stearns at dstearns@phillynews.com. Read his recent work at http://go.philly.com/

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For information on the Bethlehem Bach Festival, call 888-743-3100 or visit www.bach.org.