My only regret about the Papal Mass at Westminister was the loss of the Gregorian offertory, which too often slips away from the Ordinary Form of the Roman Rite, probably because the text is not printed in the Missal for peculiar historical reasons. Nonetheless, the Offertory proper is just as much part of the Mass as the Introit or Communion chants. Specific reference is made to it in the GIRM actually. Even in the praxis of my own parish, the offertory is probably the last on the list of chants we learn, mainly because it is a lower priority from a pastoral point of view, and also because it tends to be more difficult and time consuming in rehearsal.
And yet, there are masterpieces here. This Sunday’s offertory is an example. It is Super flumina Babylonis: Upon the rivers of Babylon, there we sat down and we wept, as we remembered you, O Zion. The chant is incredibly evocative of the text. One has the sense that one is precisely where the chant describes, by waters, weeping, remembering. See the way the chant itself looks like what it describes. The singing of such phrases requires voices of practice fluidity and expression. The word accents play a special role here, intertwining with the musical phrase with dazzling complexity.