Lenin cites this concept from Marx early in “State and Revolution.” To me, it implies that socialist states can be reformed from within to achieve communism, whereas under capitalism revolution is necessary to build socialism. I do not understand this at all. What makes post-capitalist society special in this respect? Am I misinterpreting something?
The sublation of the contradiction brings about the withering of the state, which loses its reason for existence.
As Lenin states in the first chapter of State and Revolution, the state exists to mediate the class antagonisms of society, in the interests of the ruling class of society. In a state where the dominant class is the proletariat, the state imposes itself in order to eliminate class antagonisms altogether, as this is the only way it can realise the interests of the class as a whole. Once class antagonisms are effectively abolished, there is no longer a need for a massive organisation whose role is to manage said antagonisms; when there are no outside enemies seeking to destroy you, there is no need for an enormously expensive standing army, for example.