When Pharaoh speaks to you [Moses] and says, “Produce a marvel for yourselves,” say to Aaron, “Take your staff and throw it down in front of Pharaoh. It will become a serpent.”
Allegorically, a staff signifies the direct, orderly descent of G-d’s beneficence into reality, creating and sustaining the many levels of creation as it proceeds further “down” the hierarchy of reality. A serpent, in contrast, signifies the evil of Egypt, which is simply a reincarnation of the primordial snake of the Garden of Eden.
By changing Aaron’s staff into a serpent, G-d demonstrated to Pharaoh that even evil owes its existence to G-d’s creative energy. By reverting the serpent back to a staff and having Aaron’s staff swallow the Egyptian serpents, G-d demonstrated that at any moment, He can change the serpent back to a staff, annihilating evil and making it disappear without a trace.
By realizing that evil exists solely so that we overcome it, illuminating the darkness of exile with Divine light, we personally relive the Exodus from Egypt on a daily basis, as well as hasten the final Redemption.
—from Daily Wisdom Volume 3