The Kyrie is the first Ordinary plainsong of the Mass, which is to say it uses a text common to all Mass celebrations. In the Middle Ages and Renaissance, composers of polyphony for the Mass focused on settings of the Ordinary texts, so in a Mass with polyphony, the Kyrie is usually the first polyphonic music heard in the ceremony.
Obrecht’s Kyrie I is for four voices, but he begins with a duet for superius and altus that will return at the beginning of the other Ordinary sections (Et in terra, Patrem, Sanctus, and Agnus Dei). This is called a headmotive. and serves to unify the Ordinary sections across the expanse of the Mass ritual.
In this first section of the Kyrie, Obrecht combines the text of the Kyrie, an ancient Greek prayer for God’s mercy, with a plea to St. Donatian, the name saint of Donaes de Moor. The cantus firmus is the suffrage antiphon, O beate pater Donatiane, a short chant well known to the people of Bruges. St. Donatian was the patron saint of the city, and his relics resided in the great collegiate church of Sint-Donaas.
Statuit ei, the plainsong Introit that immediately precedes the singing of the Kyrie, is a chant of general praise to any saint ranked as a Confessor Bishop. Obrecht thus brings St. Donatian to the foreground by choosing a cantus firmus that immediately declares the saint’s name and beseeches his intercession.
Obrecht also embeds a tribute to the renowned composer of the French royal court, Johannes Ockeghem, in this Kyrie. The first seven notes of the bass line are a direct quotation of the bass line in the opening Kyrie of Ockeghem’s Missa Ecce ancilla Domini, a Mass in honor of the Annunciation. Obrecht probably met Ockeghem in August 1484, when the French composer was traveling in Flanders. He makes a more overt reference to Ockeghem’s Mass in the Osanna, and indeed seems to strive to emulate the older composer’s style throughout the Mass for St. Donatian.
For more information, see:
Hiley, David. Western Plainchant: a Handbook. Oxford: Oxford University Press. 1993. See it particular pp.150-56, 211-13
Crocker, Richard L. “Kyrie eleison.” Grove Music Online. 10 Jul. 2018. www.grovemusiconline.com
Strohm, Reinhard. Music in Late Medieval Bruges. Oxford: Clarendon Press, 1985. See in particular pp. 38-42.
Wegman, Rob C. Born for the Muses: The Life and Masses of Jacob Obrecht. Oxford: Oxford University Press, 1994. See in particular pp.169-74.