As much as holiday audiences crave the soothing loveliness of Christmas music, sustaining entire programs of it is tough because the music's starting point is where most pieces end: Complete resolution of tension. It's the only sensible way to characterize the birth of Christ. And where do you go from there?

That's why choral Christmas programs by the Crossing (on Friday) and the Mendelssohn Club (Dec. 10), both at St. Paul's Episcopal Church in Chestnut Hill, were full of different musical nationalities and knew the importance of atmosphere. Both events were wonderful, in completely different ways.

Though oriented toward living composers, the Crossing's music director, Donald Nally, incorporated traditional Christmas texts such as "The Holly and the Ivy" but with reverent twists. Plainchant was juxtaposed with a pan-tonal flood of bell sound written by Gabriel Jackson, suggesting how rules changed and possibilities burgeoned with Christ's birth.

Modern Christmas poems by Joseph Brodsky, read by actors from Pig Iron Theater, went beyond the usual iconography to suggest how the Nativity looked and felt. The guiding star, for example, was the eye of God peering down on baby Jesus, who mostly slept but knew exactly what that light was.

Jackson's primary contribution was I Look From Afar, whose texts contain prayers within prayers, some of which stood out from the typical choral sounds by switching to a chanted speech in atonal harmonies. It could barely be called music, but it compellingly conveyed how humanity was on new ground.

Any number of other distinctive pieces followed, such as James MacMillan's 2010 piece Alpha and Omega, with his earthy religiosity and typically salty harmonies, plus a world premiere by Zachary Wadsworth titled Gabriel's Message, which layered a more emotionally complex harmonic world sung by the Crossing with more traditional musical bedrock sung by the choir of St. Paul's Church. More harmonically conservative pieces eschewed the usual Christmas-carol symmetry by projecting the sense of the text with great precision.

The entire concert was up to the Crossing's usual standard, but the first half sung in the candlelit church was especially mesmerizing, partly thanks to the group's sound with chords that land perfectly in tune and release with a hint of vibrato. Hear what I mean in the free download offered at www.crossingchoir.com/gift.html.

The Mendelssohn Club's program, "Golden Voices of the East," had excerpts from Rachmaninoff's Liturgy of St. John Chrysostom in which the composer subverted his big personality to strict church traditions. I hoped to hear the whole thing. Instead, traditional works by Rimsky-Korsakov and Kodaly were interspersed with periodic sing-alongs of "Silent Night" in which conductor Alan Harler was at his most irresistible. The tight, 75-minute program, and the after-concert cookies, made the event quite celebratory. Both concerts were packed - in a venue they are not known to play. Is this a phenomenon in the making?

Contact music critic David Patrick Stearns at dstearns@phillynews.com.