I very much doubt if the tune was composed in 1848, or in America, or with a Christian purpose in mind. It's quoted in Bartok's Second Rhapsody for violin and orchestra (1924, I think - at any rate long before Copland used the tune), and given exactly the same sort of treatment he used for folk tunes from eastern Europe - it's a ferocious stomping dance tune. He never used any tune from the English-speaking world, as far as I know.

My guess is that it was an old secular folktune adopted for religious purposes and taken to the US by the Moravians.