In The Mythic Image (p. 194), Campbell expounds on the full story found in Genesis. He states:
"Now it is the essence of the axial point or pole that it should symbolize the way or place of passage from motion to rest, time to eternity, seperation to union; but then also, conversely, rest to motion, eternity to time, unity to multiplicity. Hence in the Biblical Eden the image is of two trees: "the tree of life also in the midst of the garden, and the tree of knowledsge of good and evil." (Genesis 2:9) ... Adam and Eve were expelled forn the garden lest they should "take also of the the tree of life, and eat, and live forever" (Genesis 3:22)."
For those familiar with A. N. Whitehead and C. G Jung, this is a familiar concept. Whitehead called it "the method of adjusted contrasts" and Jung called it "complementarity".