It's an ideological dystopian fantasy, written in a period when everybody was doing it: Aldous Huxley in Ape and Essence, Compton Mackenzie in The Lunatic Republic, Bernard Wolfe in Limbo '90, George Orwell in 1984 - these were all written within ten years. (Walter Miller's A Canticle for Leibowitz and Pierre Boulle's Planet of the Apes were a bit later).

It would have been obvious to anyone reading it that (a) it was a parable for a particular social theory and (b) that social theories were simply another kind of fiction. The world had just been through the rise and fall of fascism, and that was just a fairytale gone horribly wrong. People didn't look to these dystopian stories for any kind of profound and life-changing message.