Checked my copy of Blues Brothers 2000 (i know, I know, the movie was so-so, but I had to have the video of the louisiana gator boys)

Anyways, the movie says that John the Revelator is a traditional piece, arranged by Son House.

The song was used twice in the movie, in the opening credits acapella by Taj Mahal. And then later in the movie by Sam Moore with a gospel chorale.

Steve