" The difficulty,” he says, “lies not in comprehending that money is a commodity, but in discovering how, why and by what means a commodity becomes money” (186): What appears to happen is not that a particular commodity becomes money because all other commodities universally express their values in it, but, on the contrary, that all other commodities universally express their values in a particular commodity because it is money. (187, emphasis added) "

― David Harvey , A Companion to Marx's Capital