Is 'in its reality' synonymous with 'in reality'?
But the essence of man is no abstraction inherent in each single individual. In its reality it is the ensemble of the social relations.
It refers to "In the reality of the essence of man" (which implies that the essence of Man is real), so it is not the same as the idiom "in reality".
What it means is anybody's guess. It seems to me to be almost a string of complex words that fail to express any clear meaning. This sort of text seems to use complex language only to obscure, not to clarify.