What you describe (money as proxy for commodity) is one school of thought that is increasingly under attack in academic circles. See for instance Money by Eric

What you describe (money as proxy for commodity) is one school of thought that is increasingly under attack in academic circles. See for instance Money by Eric Lonergan; Debt by David Graeber; Money, The Unauthorized Biography by Felix Martin; Theory Of The Monetary Circuit by Augusto Graziani; Soft Currency Economics by Warren Mossler; Creating Economic Order by Michael Hudson; Debt and Economic Renewal in the Ancient Near East by Michael Hudson. These argue that accounting systems (and even writing, according to some) grew out of interpersonal debt/credit relations. Money then grew out of these accounting systems, as a token representation of the abstract accounting entries. In this view, money is fundamentally a kind of social contract, rather than a representation of some stored potential trade-good.