This process might be called the growing spiritualization of money, since it is the essence of mental activity to bring unity out of diversity. In the sensible world, things exist side by side; only in the sphere of the mind are they integrated. The elements of a concept form a unity, as do subject and predicate in a proposition; there is no equivalent in the world of directly perceived phenomena. The organism, as the bridge between matter and mind, is the first step towards such an equivalent; interaction merges its elements and it strives constantly for an unattainable perfect unity. Only in the mind, however, does interaction become real integration. The interaction of exchange brings about a mental unity of values. The spatially extended substance is only a symbol of money, because the disconnectedness of what exists as substance contradicts the nature of money as an abstract representation of interaction. Only to the extent that the material element recedes does money become real money, that is real integration and a point of unification of interacting elements of value, which only the mind can accomplish. "
Georg Simmel The Philosophy of Money (1990 [1907]) p.198