Spinoza and Marx would seem to be two very opposed philosophers. Spinoza was interested in contemplating eternal truths of nature while Marx was interested in the history of capital.
Franck Fischbach suggests that by reading the two together we may better understand both history and nature, as well as ourselves, making possible a new understanding of human nature. Rather than see history and nature as opposed, history is nothing but the constant transformation of nature.
Central to this transformation is a new understanding of alienation not as loss of the self in a world of objects, but as loss of objects in a world that disconnects us from nature and social relations, leaving us isolated as a subject. The isolated individual, the kingdom within a kingdom, as Spinoza put it, is not the condition of our liberation but the basis of our subjection.