This is 4-part SATB harmony, "a capella". A joy to sing.
I'm not sure of the origin of this piece. My wife learned it by ear from a friend at church. Years later she sang it to me, as well as harmonies, from memory. I transcribed it with modifications.
I arranged this well-known piece for 4 men. Nothing too fancy, just 4-part harmony. One of the harmonies is above the melody (I guess you'd call it a descant).