This is the penultimate movement from my eclectic 2017 mass, Credimus, and the favorite of the conductor, Dan Booher. It functions as a reprise of the main theme from the Kyrie at the beginning, and a setup to the finale, a strangely rambunctious Southern gospel setting of the first bit of the Pascha Nostrum (with a bit of the Nicene Creed reprised for good measure).
As for this movement, it's quiet and reflective, as an Agnus Dei should be. The altos carry the melody with the basses just below, and the upper parts doing a sort of otherworldly harmonic response. The overall effect is wistful and capital-R Romantic, as Dan liked to put it--I would specify very late Romantic--and it builds to a nice long soaring note for the altos that sort of recedes into nothingness. Peace accomplished!
There exists an anthem-length version of this, with some really interesting modulations that I'm not sure I could diagram if I wanted to. We haven't performed it yet, but do stay tuned.