The text of the entire Sanctus is completed by the repetition of the phrase “Osanna in excelsis.” Composers occasionally composed new music for this textual repetition, but most, like Obrecht in this Mass, simply provide the rubric “Osanna ut supra” after the Benedictus, which means that the singers were to repeat Osanna I. The effect, in this case, is both to prolong the solemnity of this high point in the Eucharistic celebration and to offer up again the prayer for St. Donatian’s intercession.
For more information, see:
Crocker, Richard L., and David Hiley. 2001 “Sanctus.” Grove Music Online. 30 Jul. 2018. www.oxfordmusiconline.com.
Hiley, David. Western Plainchant: A Handbook. Oxford: Oxford University Press, 1993. See in particular pp. 161-65.
Strohm, Reinhard. Music in Late Medieval Bruges. New York: Oxford University Press. 1985. See in particular pp. 146-48.
Wegman, Rob C. Born for the Muses: The Life and Masses of Jacob Obrecht. New York: Oxford University Press, 1994. See in particular pp. 169-74.