The song and the album are fourteen years apart. The song made Cash’s initial reputation; the album remade his later one. The song is a studio recording of a fictional narrator; the album is a live recording in the actual place that inspired it.
When Cash opened both of the January 13 shows with “Folsom Prison Blues” — the song with which he had opened his career in some sense — the choice was deliberate. He was making a connection explicit: the person who wrote this song about a fictional prisoner at Folsom in 1953 was now standing in front of real prisoners at Folsom in 1968, performing the same song. The fifteen years between those two moments — the Sun years, the Columbia years, the drug years, the cave, the recovery, the engagement to June Carter — were the subject of the song in a new and specific way.
The line about shooting a man in Reno just to watch him die had produced a reaction from early audiences and from radio programmers. At Folsom, it produced the most distinctive reaction the line had ever received: a laugh from an audience that understood, in a way that most audiences do not, what it feels like to be in prison for exactly that kind of act. The laugh was not simple. It was the sound of recognition and something that might have been solidarity, performed by people who were in no position to find anything straightforwardly funny about their circumstances.
Cash later said he understood that moment — the audience’s reaction to that specific line — as the moment he knew the album was going to be something special.