This fantasy is the postlude from "Office de l'Epiphanie". It is a radiant piece which sums up most of Tournemire's idiosyncrasisms in "L'Orgue mystique" : rhapsodic form with contrasting sections, kinds of whirling musical garlands, repeated notes, sudden short nervous sections with brief staccato chords, harmony sometimes quite dissonant sometimes with common triads or empty fiths, large use of mixtures and mutations and, above all, use of gregorian themes which are in this case :
Alleluia for Epiphany (beginning)
Ego dormivi (at 18"")
Crudelis Herodes (at 1'44)
Omnes de Saba venient (at 2'39).