Cantus firmus setting of the hymn, given in long notes in the bass. A detailed analysis and analytical transcription is in carrasco2012-1.
The hymn, by St Thomas Aquinas, was prominent in Spain because of its use on the Feast of Corpus Christi, a particularly important feast in Spain. It is also sung on Maundy Thursday, during the procession from the church to the place where the Blessed Sacrament is kept until Good Friday. In Spain, the Mozarabic chant melody was used in preference to the standard Roman melody.