"Since Yahweh and Satan are working together, they can be considered as two aspects of the same thing, i.e., the Self. Satan provides the initiative and dynamism to set up Job's ordeal and hence represents the urge to individuation which must break up the psychological status quo in order to bring about a a new level of development. The serpent played the same role for Adam and Eve in the Garden of Eden."(Ego and Archetype, page 80, on the myth of Job)
In Christianity, Yahweh represents the Self, but only the light half. Satan is the shadow half of the Self, the part which provides the impetus for growth. It is part of the Self but, since the immature ego can't see in shades of grey, the Self must be divided up into white and black, good and evil, or Yahweh and Satan. In the same way that to a young child their parent is Good (when they give them what they want) or Bad (when they deny the child what it wants), the Self is is split into the good Yahweh and the destroyer, Satan.
The son of chaos: Satan and the role of Mercurius/the intellect.