Great chain of being
The Great Chain of Being or Scala Naturae is a medieval model of the universe and life. It outlines the perceived hierarchy of all things from the Christian god at the top down to perceived base minerals like dust.
Unchangeable vs. mutable forms
An important distinction is that between the unchangeable spirit and the changing or mutable earthly-form. In the middle of these two is the human form which contains both elements of spirit and mutable flesh. Spirit through the adherence to absolute morals is considered the path to righteousness and the primal desires of the flesh are seen to drag one away from heaven.
The concept of a Great Chain of Being rests on the existence of a Christian god and exists purely as a result of people trying to explain the role of the Christian god. It adds no compelling reason to further believe in a god.