This characteristic comes from the form of the commodity itself. This is because the social character of men's labor appears to them as an objective character stamped upon the product of that labor. The relation of the producers to their own labor is presented to them not as a social relation existing between each other. It is not presented as the product of a social form of production. Rather this social relation is presented to them as a relation between their products of their labor or things.
Social relations become relations between things.
This is fetishism. This fetishism is due to the peculiar social character of the labor that produces them. People don't produce all products together so the social nature of the production is not apparent. People only come together to exchange these products. When people exchange their products what appears to them is not a relationship connecting one individual's labor to another.