In a simple model of welfare dynamic optimisation with non-renewable natural resource where:
$$ \dot S_t = -R_t $$ $$ \dot K_t = Q(K_t,R_t)-C_t $$
one of the first order condition is that $P_t=\omega_t Q_{R}$, where $P_t$ is the shadow price of the natural resource stock $S$, $Q_{R}$ is the marginal product of the natural resource and $\omega_t$ is the shadow price of the human-capital stock $K$.
In the Perman et al. (2011) "Natural resource and environmental economics" this equation is explained as "the marginal value (or shadow price) of the natural resource stock must be equal to the value of the marginal product of the natural resource". In particular $\omega_t$ is redefined as the value of one unit of output, with the justification that units of outputs and units of capital are in effect identical in this economy among the optimal path, as any output that is not consumed is added to capital.
It is this redefinition that I do not understand.