This is either a lovely Kyrie for an assembly or a stern test for your cantors. “Have mercy” indeed. Luke D. Rosen used the Sarum Missal for his verses. The 3/4+4/4 setting is marvellous if annoying to program into Band In a Box! It is a new addition in Breaking Bread for 2023.
You could put your choir to work during a second Rite of Reconciliation or find a place for it in Lent.
The sheet music can be purchased at OCP where the text is in their preview.
My backing puts the ostinato refrain on one side and the cantor part on the other for learning purposes.
Doing this litany at Gethsemane, as above, would just about done me in I think.