In section 17.4, Keynes further examines the singular combination of characteristics which distinguishes money from other commodities, in terms of the dynamics of an arbitrary commodities rate of interest in terms of itself. He is illustrating why the interest rate of money is the most systematically significant rate of interest, and why our economy revolves around it and not around the rate of interest in terms of some other commodity. This is all part of his examination of money and interest, and how they factor into the macroeconomic complex that is his general theory.