One of the best-selling pieces of choral music of the late twentieth century, the motet "O Magnum Mysterium" ("O Great Mystery") epitomizes the style of its composer, American Morten Lauridsen. In this four-part a cappella chorus work, Lauridsen takes a centuries-old Latin text describing the Nativity scene, imbues it with closely-voiced chords, colored by suspensions or quietly dissonant tones, and creates a restrained, simple setting that develops at an unhurried pace.
Against a chord sustained by the soprano, tenor, and bass voices, the alto introduces the disjunct melodic line for the title phrase, a melody of which Lauridsen was fond enough to bring back in his later composition "Lux Aeterna". The phrase is transposed and repeated, and the melody is now heard from the tenors.
The heavily homophonic nature of the piece gives it the feel of chant at times, and as the title phrase overlaps into the next section, "et admirabile sacramentum" ("and miraculous sacrament") the voices, particularly the soprano, are indeed melismatic. After this longer section, the opening material returns intact, and again leads smoothly into the subsequent text, "ut animalia viderent Dominum" ("that the animals should see the Lord"), and again is heard the music from "et admirabile sacramentum". The section is closed by a hushed "jacentem in praesipio" ("lying in the manger").
For the final section of text, beginning "Beata Virgo" ("Blessed Virgin"), Lauridsen shifts to triple meter, and a gradual swell begins, finally culminating in a return to the opening music. This time, however, the parts are divisi and the texture is more majestic, the mood more deliberately passionate; before a sense of wonder, here a sense of joy. A brief coda on "Alleluia" is grafted seamlessly onto the section; its melody is clearly drawn from the "O magnum mysterium" motive. The piece subsides into a hushed close.
Apart from the lack of counterpoint, the setting uses all Lauridsen's touchstones: chord voicing, formal organization, even his favorite key, D major. The first work performed by the Los Angeles Master Chorale after Lauridsen was appointed their Composer in Residence, "O Magnum Mysterium" was premiered by the chorus at their Christmas concert in 1994.