I know this is obvious, but Cash's beliefs are endlessly fascinating. The same man who recorded "Ragged Old Flag" also wrote "Man in Black" and covered "Out Among the Stars." The latter is a song about a kid who commits suicide by cop because he doesn't feel like his life matters.
All of Johnny's covers are fantastic. His cover of Tom Petty's Won't Back Down with Tom singing backup vocals, for example.
Honestly that song always brings a tear to my eye.
His rendition is a masterpiece.