In section 16.2, Keynes grounds his theory of production in labor, set in a context of other factors of production, such as technical efficiency of capital equipment, effective demand, etc.
He also goes on to argue that the interest rate exerts a determining force on the optimum length of production processes, which are generally centered around delivering output to consumers at the time of effective demand, i.e. when the aggregate demand function coincides with the aggregate supply function - which is the general theory’s way of saying when demand meets supply (which the general theory argues isn’t always the case, against the assumption of the classical theory). He also says that the value of capital is better understood in terms of its prospective yield relative to its supply cost, and that its scarcity contributes to this capital efficiency.