Marginal rates of substitution between goods in the same state are equal across individuals.
Marginal rates of substitution between goods in different states equal a constant times the marginal rate of substitution between the numeraires in the different states. With complate markets they are also equal.
Since individuals' marginal rates of substitution of wealth across states are pinned down by asset price ratios, all MRSs are equal, and so equilibrium is Pareto optimal.