The theme of blues music is oppression. This is most obvious in the lyrics, which speak of the suffering and pain caused by events outside of the singer’s control. Oppression is also expressed in the heartfelt vocals of the singers. It is even present in the form of the music itself, chained as it is to a fairly rigid song structure and limited chord progressions. You can see it in the structure of the lyrics, in the way that an initial statement of a condition is often repeated in the second line of a verse, without modification.
The great theme of jazz, on the other hand, is freedom. Jazz musicians most often start with a popular song, state the melody, and then go on to improvise variations. The musical statement is clear: I can be free, I can express my own personal identity, even when working within the confines of a structure that is not mine. Every variant note, every swinging chorus, every improvisational foray, restates this basic theme of freedom. Even when starting with a blues structure, the implication is different, because the song is only a point of departure. As John Litweiler says in The Freedom Principle: Jazz after 1958, “The quest for freedom with a small f appears at the very beginning of jazz and reappears at every growing point in the music's history.” (Litweiler 1990)
The theme of rock music, as I will show, is liberation: release from constraints of every kind. In a way, then, rock is positioned precisely between the blues and jazz. Blues captures the state of oppression, while jazz expresses the opposite state of freedom. Rock does not express a fixed state at all, but captures the transition, the movement from one state to another, the act of throwing off the chains.