Reinhold Niebuhr believed that certain central myths of Scripture should be taken "seriously but not literally, e. g., Creation, Incarnation, and Last Things. "Seriously" means that these myths convey truths and meanings essential to "biblical faith." Who determines what these truths and meanings are? Reinhold Niebuhr, of course. So RN uses these myths as a vehicle for transmitting his view of essential biblical truths. He is no different from any other theologian. Theology is the expression of religious belief. The Nature and Destiny of Man, 2 vol. is the best source for Niebuhr's thought
Rudolf Bultmann thought that myth meant (1) prescientific cosmology, e. g., three-story universe, miracles, etc. and (2) use of spatial metaphors for transcendence. God is up in heaven means that God is transcendent to people and earth. He thought he had to find the religious meanning in the myth taken in non-supernatural terms,
RN thought that RB reduced biblical myth to Heidegger's philosophy of existence, specifically human existence. RB therefore lost something essential to biblical truth, according to RN.
This is for my friend Ben Jordan and others who are interested.