From Wikipedia:

The lyrics
"Simple Gifts" was written by Elder Joseph while he was at the Shaker community in Alfred, Maine in 1848.
Several Shaker manuscripts indicate that this is a "Dancing Song" or a "Quick Dance." The references to "turning" in the last two lines have been identified as dance instructions.
The song was largely unknown outside of Shaker communities until it became world famous thanks to its use in Aaron Copland's score for Martha Graham's ballet, Appalachian Spring, first performed in 1944. Copland used "Simple Gifts" a second time in 1950 in his first set of Old American Songs for voice and piano, which was later orchestrated. Many people thought that the tune of "Simple Gifts" was a traditional Celtic one but both the music and original lyrics are actually the compositions of Brackett. Adaptations and extensions of Brackett's original lyrics have occurred and actually are in the public domain.

Aaron Copland
(November 14, 1900 – December 2, 1990) was an American composer of concert and film music, as well as an accomplished pianist. Instrumental in forging a distinctly American style of composition, he was widely known as "the dean of American composers." Copland's music achieved a balance between modern music and American folk styles. The open, slowly changing harmonies of many of his works are said to evoke the vast American landscape. He also incorporated percussive orchestration, changing meter, polyrhythms, polychords and tone rows in a broad range of works for concert hall, theater, ballet, and films. Aside from composing, Copland was a teacher, lecturer, critic, writer, and conductor (generally, but not always, of his own works).