For a movie that is so scrupulously accurate in so many respects, "Walk the Line" makes surprisingly little of the abiding faith that Mr. Cash always credited, along with Ms. Carter, for saving his life. "That dimension of Cash's life, which was present all the way through, was absent," said the Rev. C. Clifton Black, a professor at Princeton Theological Seminary, who criticized the film for that reason in a review for the magazine The Christian Century. "I was stunned."