A 14th-century mystic struggles to capture a divine melody until an unlikely animal companion intervenes. Brother Heinrich, a Dominican mystic, seeks to transcribe the celestial carol 'In dulci jubilo' as it is revealed to him by angels. He faces the logical constraint of human limitation in recording divine inspiration, while his donkey, Sigismund, provides the necessary grounding to complete the task. The narrative framework functions as a musical fable, designed to be performed by a narrator, choir, and instrumental ensemble.

Readers and listeners often appreciate the whimsical tone that John Rutter brings to this historical legend. Discussion frequently centers on the effective blend of musical composition and storytelling, which makes the work accessible for holiday performances. Critics highlight the charm of the donkey character, Sigismund, as a grounding force that balances the ethereal nature of the mystic's experience. The work is widely regarded as a staple in choral repertoires, with many noting how the narrative structure enhances the emotional resonance of the music itself.