This arrangement is of another arrangement by an anonymous figure from the 16th Century. The four part setting of the Gregorian chant of the same name can be found in the Cancionero de Upsala [sic], a volume of Spanish music printed in Venice in 1556. The only original copy is kept at the Uppsala University Library, hence the name.
The version from the Cancionero uses, as the basis of its refrain, the Latin phrase 'Verbum caro factum est' (from The New Testament, John 1:14). Interspersed are verses in Spanish, one as though sung by the Virgin Mary to her newborn child, another as a response to her question and a challenge to the listener which might be interpreted as a call to charity over the Christmas period.