In addition to their individual self interest, rational beings have a spiritual self interest, because there are goals that are good for their spiritual animal and the rational subject is responsible for pursuing them. Since spiritual self interest may conflict with individual self interest, there are priorities among the goals that are good for reason.
There are goals that are good for spiritual animals, because spiritual animals evolve by imposing natural selection on themselves at the social level of biological organization at the same time that their members are evolving as individual by reproductive causation at the multicellular biological level. These goals are good for the spiritual animal because attaining them contributes to the natural perfection of the spiritual animal.
Necessary goals of spiritual interest are social level goals the attainment of which would control conditions that affect the reproduction of the spiritual animal. Reproduction itself is not a necessary goal of spiritual interest, but merely what determines which goals are necessary to be in a position to reproduce, if the occasion should arise.
As animals on the social level of biological organization, spiritual animals have behavior that acts on other objects in space to control such relevant conditions as supplying free energy and other resources and protecting them for natural dangers. But among their external necessary goals are goals having to do with war and peace with other spiritual animals, since the possibility of war makes that a condition that affects social level reproduction.
Spiritual animals have internal goals, as well as external goals, because in addition to acting on other objects in space, they must also pursue goals by which they act on their own members. In spiritual animals, reason serves as a biological as well as an animal behavior guidance system. Internal goals control such conditions as coordinating productive behavior, distributing resources, enforcing laws, and education.
Since spiritual animals are rational beings, reason gives them the autonomy to pursue goals simply because they believe that they are good. With more power than they need to control conditions that affect their own social level reproduction, spiritual animals can make goals good for themselves by choosing to pursue them (when they are already good for contributing to the natural perfection of things other than themselves). Optional goals may include protecting endangered species, assisting other spiritual animals, controlling the causes of war, and the like,
Individual and spiritual interests are equal, because each contributes to natural perfection on its level of biological organization. But goals that are good in both ways are good for rational subjects, because they are the agents of reason. Thus, there must be priorities for choosing among goals serving individual and spiritual self interest when they conflict. And given the symmetry between these interest, there are two kinds of priority rules.
Moral rules limit the pursuit of individual self interest by limiting how rational subjects can pursue their goals and which optional goals they may pursue. The general observance of moral rules is a necessary goal of spiritual animals, because it is a condition of being able to pursue spiritual goals at all. Rational subjects ought to be moral, because necessary goals of spiritual self interest take priority over optional goals of individual self interest.
Rules of justice limit the spiritual animal's pursuit of social level goals by limiting how they may pursue necessary goals and limiting which optional goals they may pursue. The observance of rules of justice is a necessary goal of individuals, because it is a condition of their willingness to cooperate in generating social level behavior. Rational beings ought to observe limits of justice, because necessary goals of individual self interest are prior to optional goals of spiritual self interest.