I don't think the Philadelphia Chamber Music Society had ever started a concert like this before.

PCMS artistic director Miles Cohen stepped before the audience at the Church of the Holy Trinity on Friday night, gave his usual affable curtain speech, and told us that, at the performers' request, the concert would not start for another 10 minutes. We gradually realized that people in black were at the front of the church, passing lit votive candles to each other and spreading them about the floor as a pianist played slow, spare music sounding like Arvo Pärt.

The candle-bearers were, of course, the singers of the Crossing, and the occasion was the group's annual holiday concert, the Crossing @ Christmas. The prelude was improvised by keyboardist John Grecia; he and his colleagues used the piano, small bells, and a tuned water glass to provide soft, solemn interludes between each piece.

Anchoring the program was Kevin Puts' To Touch the Sky, a nine-movement cycle on women's texts from Sappho and Christina Rossetti to Hildegard of Bingen and Mother Teresa. Most striking was At Castle Wood, based on an Emily Brontë poem almost Russian in its bleak fatalism; Puts' music isn't grim or grief-stricken, it's clear-eyed and resolute.

A great dissonant organ blast opened the evening's world premiere, Aaron Helgeson's A way far home, in which fragmented phrases circle around the word and idea of home - leaving it, longing for it, arriving at it, being driven from it. The voices swirl those phrases around under a high-pitched, quietly tense two-note organ drone, each stanza ending in "home" or "go" - the word falling apart as the voices slide downward and dissolve. An organ blast recurs between each stanza - except when it doesn't. Yes, it's an elusive and disorienting piece, and more powerful for it. (Helgeson's program notes may be the most beautifully written I've ever seen by a composer.)

At the heart of the evening were two brief, tender scores by David Lang: "where you go", a gently impassioned setting of Ruth's pledge to Naomi from the Old Testament; and, both opening and closing the program, "last spring," an old man's remembrance of what may be his final season, his memories gradually subsumed into a stream of overlapping voices repeating "more time."

The Crossing's concerts are such collaborative efforts that there's rarely a single star performer, but on Friday, soprano Rebecca Siler was a marvel. Whether sailing through a lead melody, floating a sustained high note, or soaring above her colleagues with a descant line, her singing was as brilliant, pure, and precisely pitched as a laser.