I don’t think it has to be understood, in fact I think this is a thing that stops people from listening initially, that they are frightened that Jazz has to be engaged with on an intellectual level. If you dig it then great, if you don’t, no worries but I think the appreciation of Jazz purely on a dig it or don’t level is as important as understanding it. My Mum *spits* had no musical ability or theoretical understanding of Jazz but she turned me on to Brubeck, Ellington, Miles Davis loads of stuff.