I don't think that the versions I saw had the Morgan Freeman type narrator, or at least I don't remember that. I think the theatrical versions I saw unfolded the story more through the characters and the music with less narration. Having said that, it was fun to see Morgan Freeman, especially after having seen Invictus a few days ago. The music is phenomenal, of course, with the Five Blind Boys, the Soul Stirrers, The Steele's, and Robert Earl Jones (the father of James Earl Jones, who was Darth Vader among many other roles).
At some point during the 1990s, after seeing the Gospel of Colonus for the first time, I read the three Theban plays of Sophocles, Oedipus the King, Oedipus at Colonus, and Antigone, in the Robert Fagles translation. Gospel of Colonus is based primarily on Oedipus at Colonus with maybe a little bit of the others mixed in. This part of the story happens long after Oedipus married his mother (although he didn't know she was his mother) and killed his father (although he didn't know he was his father), the parents having abandoned him at birth because of the prophecy of an oracle. Oedipus, of course, blinded himself when he found out the truth and took himself off to exile. One thing I would emphasize is that Oedipus was a (fictional) King but wasn't a "greek god."
Needless to say, Oedipus' story is an incredibly dramatic one--not a "biblical" story exactly but an incredibly profound and dramatic one. Borrowing the "gospel" style of music to re-tell this story was an incredibly brilliant choice--the resulting story has a lot of contemporary relevance, I'd say. I would think that anyone could appreciate the "energy" of the music in the Gospel of Colonus without knowing much if anything about Oedipus and all that.