The sixth characteristic of cultural purpose that distinguishes it from internal and proximate purpose is desirability or perceived value. Again internal purposes of self-perfection or making a good life for oneself don’t involve a question of desirability which is intrinsic to the meaning of purpose there. Similarly, with respect to romantic interests, family, and friends, only desirable purposes make much sense. This is less true at the level of acquaintance or stranger where one might imagine purpose in taking advantage of others, but then ethical considerations should intervene. However with respect to societal purpose, desirability becomes to some extent the dominant criterion. 
This is not simply a matter of magnitude; it took much more effort to create the atomic bomb than the first airplane, but most of us would choose to have devoted our life to the latter rather than the former, that is, proof of the possibility of human flight appears heroic, while demonstration of the destructive force of the atom is abhorrent even if ultimately defensible.
The last feature of purpose at the level of cultural reality not reflected in internal or proximate reality is necessity, or more accurately absence of necessity. It seems to me that we must find purpose with respect to the self and to others (again unless you choose to be a complete hermit), but choice at the level of cultural reality includes the potential choice not to devote oneself to any societal purpose at all. Unlike the hermit who forsakes humanity, an otherwise socially involved individual may choose to devote his or her life to cosmic purposes such as saving an endangered species or studying astronomical phenomena with no practical applications. 
While there may be indirect cultural benefits, these are secondary, and missions of this type are more accurately assigned to the level of cosmic reality. Simply stated, you don’t devote your life to save the polar bear from extinction because it is good for humanity, but because it is good for polar bears. Society understands and respects such choices.
In short our purpose in the human world is one we choose based on considerations of feasibility, calibrations of significance, personal satisfaction, and external appeal. We may adopt multiple purposes within our community, nation, world, or history or we may defer cultural purpose altogether in favor of cosmic purpose. However we must accept that meeting our own need for self-esteem and lasting significance compels us to identify and pursue one or more cultural or cosmic purposes. A meaningful life is the reward for the effort we make and risk of failure we take as one more link in the long chain of human achievement.
