I was inspired to listen to this piece after a great rendition of it was performed by the DePauw Chamber Singers this afternoon.
It begins softly with the sopranos and altos. mostly, the altos sing static notes, changing notes chromatically within the phrase. the sopranos have the main melody, which is taken over by the tenors and basses when the first phrase ends. when the tenors and basses are through with their solos, the females and the males come in together, much louder this time and even more expressive. i love listening to the changing lines and the contrast between the voices. it's pretty magical, not gonna lie.
I like to think of this piece as having the shape of an arc because it begins so softly, then loudens gradually, and tapers off at the end with a pretty sweet plagal cadence (when they all sing a----men) .