"Will the Circle be Unbroken", covered by Ralph Stanley.
While the song was originally an early 20th century hymn, it is a wonderful example of early American folk music when performed in a "Bluegrass format". Earlier American folk music often has strong themes of God and family, which continue to play a role in modern Bluegrass, and often modern Country and Western music.
The man performing the song, Ralph Stanley, has been active in the Bluegrass circuit for over 65 years, is still very much alive (87 years young), and still actively tours. I was able to see him perform live a few years ago here in Phoenix, and it was an absolutely wonderful experience.