Capitalist production therefore reproduces in the course of its own process the separation between labor power and the conditions of labor. It thereby reproduces and perpetuates the conditions under which the worker is exploited. It incessantly forces him to sell his labor power in order to live, and enables the capitalist to purchase labor power in order that he may enrich himself. It is no longer a mere accident that capitalist and worker confront each other in the market as buyer and seller. It is the alternating rhythm of the process itself which throws the worker back onto the market again and again as a seller of his labor power and continually transforms his own product into a means by which another man can purchase him. In reality, the worker belongs to capital before he has sold himself to the capitalist. His economic bondage is at once mediated through, and concealed by, the periodic renewal of the act by which he sells himself, his change of masters, and the oscillations in the market price of his labor.
The capitalist process of production, therefore, seen as a total, connected process, i.e., a process of reproduction, produces not only commodities, not only surplus value, but it also produces the capital-relation itself: on one the hand the capitalist, on the other hand the wage laborer.
Karl Marx, “Simple Reproduction [of the Process of Accumulation of Capital]”, in Capital, Vol. I, trans. by Ben Fowkes, New York: Penguin, 1990, pp. 723-724.