The Great Chain of Being (Latin: scala naturae, "Ladder of Being") is a concept derived from Plato, Aristotle (in his Historia Animalium), Plotinus and Proclus. Further developed during the Middle Ages, it reached full expression in early modern Neoplatonism.
The Chain of Being is composed of a great number of hierarchical links, from the most basic and foundational elements up through the very highest perfection: God.
God sits at the top of the chain, and beneath him sit the angels, both existing wholly in spirit form. Earthly flesh is fallible and ever-changing, mutable. Spirit, however, is unchanging and permanent. This sense of permanence is crucial to understanding this conception of reality. It is generally impossible to change the position of an object in the hierarchy. (One exception might be in the realm of alchemy, where alchemists attempted to transmute base elements, such as lead, into higher elements, either silver or, more often, gold—the highest element.)
In the natural order, earth (rock) is at the bottom of the chain; this element possesses only the attribute of existence. Each link succeeding upward contains the positive attributes of the previous link and adds at least one other. Rocks possess only existence; the next link up is plants which possess life and existence. Animals add motion and appetite as well.
Man is both mortal flesh, as those below him, and also spirit, as those above. In this dichotomy, the struggle between flesh and spirit becomes a moral one. The way of the spirit is higher, more noble; it brings one closer to God. The desires of the flesh move one away from God. The Christian fall of Lucifer is thought of as especially terrible, as angels are wholly spirit, yet Lucifer defied God (who is the ultimate perfection).