>>578775money is a socially constructed abstraction of the money commodity, and the money commodity was traditionally a good, like precious metals, which were portable, slow to decay, and took a lot of socially necessary labor time to produce (i.e. mine and refine in the case of metals). this abstraction became useful because it allowed for a "universal third good" to mediate exchange between any two arbitrary parties. Once banks became larger and more centralized, paper money developed which was a further abstraction. They started off as guarantees of repayment (IOUs) in the form of money commodities, but once they became decoupled from the standard of any precious metal, you had fiat. Digital currency is simply another layer of abstraction on top of fiat.
TL;DR all money is just a socially constructed abstraction of the socially necessary labor time required to produce a commodity, and socially necessary labor time is itself an abstraction of labor itself.
Abstraction is necessary for society to exist, and comes in many forms. But it always isolates the things humans want to focus on and removes the things which are more circumstantial.