This song basically revoices the sophomoric apologetic for war--or state-sanctioned murder in general--that war is a part of human nature and, as such, is a kind of unstoppable force that we inveigh against at the cost of looking silly; this is the basic meaning of the bullet line/title, "Blame It On Cain;" blame it on human nature, inherited from the legacy of Cain.
Well, this song sort of turns the tables on this idea. It points out how this trueism only serves the interests of the State; how does it sound coming out of the mouth of a common peasant? When farmers and working people get sick of being ripped off and take matters into their own hands (e.g., Central America, circa 1950s/60s), are we going to "Blame It On Cain" then? Why shouldn't we?
This song cleverly points out a chief hypocrisy of that view.
Beside this, the song also paints a word picture of the high hopes of the central character ("Well, if I was a saint..."). This only underscores the fact that underlying all this bitterness is a positive and humanizing longing for heavenly treasures and its natural concomitant, a recognition of rights.