The rod cast down becoming a serpent is the spine's own power released along its channel, the coiled energy at the base of the body rising into visible form. Aaron's staff is the backbone, and when it is laid before the ruling ego it turns into the serpent that has always slept there, the creative fire the ancients drew as a snake. Pharaoh is the hardened lower mind on its throne, confronted in its own chamber by the force it thought it governed.
The backbone holds a coiled power that the higher command brings forward. Laid down before the ruling self, that power shows its living form, and the ego watches the serpent it never controlled.
The rod: the human spine, the straight staff of the backbone that carries the body's rising power.
The serpent: the coiled energy at the base of the spine, the creative fire the old teachings drew as a snake.
Pharaoh: the hardened ego enthroned in the lower mind, ruling the body it believes it owns.
Aaron: the faculty that speaks and acts for the higher will, casting the spine's power into open view.