I recently saw the movie, Walk the Line. I realize that I am late to this party, but, hey, I have young kids. before I saw the movie, I was aware of complaints from some religious viewers that the religious side of Johnny Cash was largely left out of the biopic. I must agree, but not with a qualification.
I knew that Johnny Cash was religious, and I also knew that he was a hell-raiser. This dichotomy is not too rare in the South. I didn't miss the religious element very much because the movie covered part of his life when Johnny was not very religiously inclined.
Right at the end, though, the movie did make it seem that June Carter and the Carter family were mostly to credit for his turnaround. In fact, there was a long, montagious shot where he is at the depths of despair that could have easily concluded at the Nickajack cave (which happened in late '67, just before the end of the period the movie covers.)
I googled Johnny Cash after the movie was over because I assumed that at some point he had a moment of embrace of religion. That's when I read about the Nickajack cave episode where Johnny went as his (first) marriage was dissolving and he intended to commit suicide by wandering into the cave and getting irretrievably lost. In the cave, Cash says he had a vision of light and heard the voice of God say that He wasn't through with Cash yet. And then the way out of the cave was made clear to Cash by a light and wiff of air. He addressed this episode in detail in his autobiography. He wasn't a perfect religious man after this incident, but he clearly points to it as transformative. It would have fit easily into the movie. It seems to have been left out on purpose by the filmmakers to avoid the uncomfortable inclusion of religion.
That is unfortunate. To be honest, revelatory religions, such as Christianity, generally infuriate me. So I am no disgruntled Christianist, but it is pretty clear what Johnny Cash thought was important in his life, and his story is not complete without Nickajack Cave. The filmmakers were cowards, and probably not very good business men either, given The Passion of the Christ's billion dollar box office take. Again, unfortunate.