Gregorian chant is the name given to the style of sacred monody that developed primarily during the ninth and tenth centuries. O admirabile commercium is sung as the opening of Vespers at the Octave of Christmas (January 1). The simplicity of the melody helps lend to the importance of this declamatory text.

O admirabile commercium! 
Creator generis humani 
Animatum corpus sumens,
De virgine nasci dignatus est: 
Et procedens homo sine semine, 
Largitus est nobis suam deitatem. 

O wondrous exchange!
The creator of the human race,
assuming a living body,
has designed to be born of a virgin
and, becoming man without human seed,
He has bestowed upon us his divinity.

Program notes by Matt Niess, Matt Oltman, Vince Peterson, Dina Spyropoulos, Noah Wagar and Drew Young