The Post-Communion is the final chant of the Mass, followed only by the formal dismissal. It begins with an ancient salutation formula, a short exchange of phrases between celebrant and choir before the celebrant intones the body of the prayer in an austere recitational style akin to that employed for the Collect prayer.
In almost all Masses, the text of the Post-Communion, which is Proper to the occasion, refers back to the Communion itself, and specifically to the communion of the congregation – even when, as in the 15th century, congregational communion was rare. The Post-Communion is both a prayer of thanksgiving for participation in the mystery of the Eucharist and a petition to God for access to the heavenly kingdom. In Post-Communion prayers for saints’ feasts, the honored saint is usually referenced in the same manner that St. Donatian is here – with the addition of the phrase “intercedente beato Donatiano” or “through the intercession of St. Donatian” before the request for God’s grace.
Anna DeLoi with M. Jennifer Bloxam
To learn more about the Post-Communion, see:
Jungmann, Joseph A. The Mass of the Roman Rite: Its Origins and Development, Vol. 2. New York: Benzinger Brothers, 1955. See in particular pp. 419-25