Not really my era, but i think that might be the Barber - Adagio For Strings.Thal
I never heard a choir version of that but it is definitely the melody from Barber's Adagio for Strings (famous from the movie Platoon). The Barber piece is a whole step higher than this, but the same intervals.
He rewrote the adagio for strings as a mass.I say he rewrote it, it was more like just sticking the words in, can't have taken him more than maybe twenty minutes to do.Works though.