Rosa Luxemburg,
The Accumulation of Capital
“ Money there had an ephemeral part, mediating the distribution of the social product among the various groups of consumers—the agent for the renewal of capital. In the process of accumulation, however, the money form has an essential function: it no longer serves as a mere agent in the circulation of commodities—here it has come to be a feature of capital itself, an element in the circulation of capital. Even if the transformation of the surplus value is not essential to real reproduction, it is the economic sine qua non of capitalist accumulation. ”
