According to WideOpenCountry.com, “Just weeks after the song’s 1956 release, Johnny Cash performed ‘I Walk The Line’ at the Grand Ole Opry and was met with thunderous applause and a standing ovation. Audiences instinctively connected with Cash’s unique track and vocals while musicians tried to put into words what was so special about Cash. ‘It was different than anything else you had ever heard,’ Bob Dylan told Rolling Stone. ‘A voice from the middle of the Earth.’ And NPR quotes Cash’s former son-in-law Rodney Crowell as saying, ‘You know, if Mt. Rushmore could open its mouth — any one of the sculptures on Mt. Rushmore could open their mouths and sing, that’s what it would sound like.’
WideOpenCountry reports that the song “stayed on the country charts for a solid year and sold over 2 million records. It even showed up on the pop charts for a while, giving Cash a bonafide crossover hit.”
Lacking a traditional verse/chorus structure (unless “because you’re mine/I walk the line” constitutes a chorus all on its own), the bare-bones tune takes a standard three-chord structure and jumps it through multiple modulation hoops. In the process of all of the key changes, we get a full tour of Cash’s bass/baritone vocal range, covering over two octaves.