The lonely hour of the final instance never comes. This seemingly delphic statement has a fairly simple meaning.
Marxists speak of social life being determined 'in the last instance' by the economy, by the manner in which people go about producing their means of existence. In capitalist society, this production is structured around a fundamental antagonism, or 'contradiction', between capital and labour. Yet there is no point at which this antagonism appears in its stark simplicity; no mise-en-scene in which the multiple contradictions and determinations that make up a social formation (think of gender, ethnicity, religion, regional divides, culture wars, and so on) suddenly step aside, and give the stage to the real, fundamental contradiction. The elements of a social formation continue always to have a reciprocal effectivity, so that each element is overdetermined by the whole. The class struggle always has cultural, national, gender, religious, identitarian or other inflections. This is why the 'pure' class struggle never arrives, any more than does the 'pure' revolution.