Forces amassed Friday night to perform Mendelssohn's oratorio "Elijah," covering the stage to overflowing and producing a sonic grandeur unmatched in recordings.

The 10th Annual Hawai'i International Choral Festival by the O'ahu Choral Society brought together (take a deep breath): the Honolulu Symphony Chorus, under Interim Chorus Director Nola Nahulu; the American Samoa Community College Chamber Singers, directed by Director Namulau'ulu Paul V. Pouesi; the Hawaii Youth Opera Chorus and the Scelto and Na Leo Kuho'okahi Ensembles, all three directed by Nahulu; the University of Hawai'i Chamber Singers, directed by Esther Yoo; five soloists; and the Honolulu Symphony, the whole conducted by Sir David Willcocks.

Among major classical music genres — symphonies, operas, concertos — oratorios are surely the least well known. Many listeners know barely a handful, which suggests that these glories of choral literature are either headed toward oblivion or poised for a comeback.

Judging from the reception Friday night, the O'ahu Choral Society is staging a comeback, and Mendelssohn's "Elijah" provided a persuasive choice.

The soloists — baritone Leon Williams, tenor Alan Bennett, mezzo Margaret Lattimore, and soprano Karina Gauvin — were wonderful: excellent voices, excellent articulation, clear, well-matched, perfect for storytelling.

Highlights included two stellar duets by Williams (Elijah), "It is enough!" a moving lament with the cello, and "For the mountains shall depart" with the oboe; Bennett's "Man of God" (Obadiah); Lattimore's "Woe, woe unto them" in Part I; and Gauvin's "Hear ye, Israel" opening Part II. Gauvin, as the widow holding her dead son, tapered to a heart-wrenching pianissimo on the line "There is no breath in him!"

The part of the Youth, usually a soprano role, was sung by boy soprano Charles Mukaida from the edge of the balcony, in dialogue with Elijah on the stage.

In fact, Friday's performance featured several antiphonal passages. One of the most beautiful came in "Lift thine eyes," sung not as a trio, but as a three-part female choir of Angels, split between sides of the balcony. The choir had a lovely vocal timbre and held together despite the challenges of singing so far apart.

Throughout, the massed choirs recreated the ancient story, as pagans, angels, converts, moralizers — the consummate storyteller, the fabric from which each aria emerges.

For oratorio to flourish again, audiences will need to re-learn the fine art of listening to the genre, which poses demands and proceeds unlike other dramas.

First, oratorio assumes intimate familiarity with the Christian Bible: it does not tell a story so much as comment upon it.

Oratorio also intermingles narrative functions, the same singer or ensemble slipping between narration, the dramatic portrayal of events, and reflective interludes. Those unfamiliar with the Bible rely on program notes and supertitles for explanations.

Because the story unfolds simultaneously in music and mind, the audience becomes part of the performance, "living" within the musical tale, re-enacting it vividly in their imaginations, savoring individual moments, reflecting upon the story and learning from it. And the music, in turn, becomes the soundtrack to their imaginations.

Finally, oratorio revels in musical depiction, a particular skill of Mendelssohn's. In "Elijah," curses come out in angular melodies with heavy bass lines, multiple independent parts simulate pandemonium, a hushed tutti pianissimo conveys awe, and huge, consonant chords signal religious conversion.

The story of Elijah offered Mendelssohn ample material: a tempest, an earthquake and a fire (all in one chorus!), a whirlwind, miracles, and more. In one confrontation, the pagans call upon their god, Baal, in a choir with minimal bass, so that their cries sound noisy, tinny and shallow, while Elijah calls upon his God in a warm legato of simple beauty, the chords balanced with a firmly grounded bass line.

Oratorio is an unhurried, interactive experience quite unlike other genres, and Mendelssohn's "Elijah" is a work that bears multiple rehearings.

Friday's audience evidently agreed, leaping to their feet in an enthusiastic ovation as the final chord faded.