O Magnum Mysterium is an a cappella SATB setting of the Christmas responsory. I constructed this work in three sections to mirror the text: the wonder of the Nativity, the celebration of Mary, and the joyful Alleluias.

I devised an original theme in G minor, slow and hushed at the opening, befitting the responsory that contemplates the mystery of animals witnessing the newborn Lord in the manger. The sopranos state the theme, with other voices gradually joining in, culminating at the final repeat of mysterium (“mystery”) in a surprising G-major cadence, low and soft. Basses pick up the next phrase, et admirabile sacramentum (“and wondrous sacrament”), again with the other voices gradually adding to the sonority, swelling to a peak at sacramentum.

The mood darkens at ut animalia viderent (“that animals should witness”), presented by the full choir. A delicate hush descends at jacentem in praesepio (“lying in a manger”), marked sotto voce. The voices swell on the repeat of the text, coming to rest on a placid B-flat-major chord.

The middle section, Beata Virgo (“blessed is the virgin”), introduces a contrasting F-minor theme, setting apart the text’s turn toward the Virgin who bore Christ. Altos introduce a new theme, now treated in a more contrapuntal style. The music begins a long crescendo at portare Dominum Christum (“to bear the Lord Christ”), leading to an outburst of melismatic emotion at the repeat of portare, dimming to a quiet F-major cadence on Christum.

The Alleluia section returns the harmony to G minor using the opening theme, but much quicker this time, and marked gioioso. Calls and responses between the women’s and men’s voices brighten to G major before closing in B-flat, the home key’s relative major, signifying an opening out into joy after the work’s meditative beginning.

Here are the Latin and English texts: