Exodus 7:9 - Joseph Benson’s Commentary on the Old and New Testaments

Say unto Aaron, Take thy rod This Moses ordinarily held in his hand, and delivered to Aaron, upon occasion, for the execution of his commands. For this and some other miracles were to be done, not by Moses immediately, but by Aaron, partly, perhaps, to preclude or take off the suspicion that these miracles were wrought by some magic arts of Moses, and partly for the greater honour of Moses, that he might be what God had said, (Exodus 7:1,) a god to Pharaoh, who not only could work miracles himself, but also give power to others to do so. Perhaps the conjecture of Grotius upon this place may be worth mentioning here, which is, that the custom of ambassadors bearing a caduceus, or rod, in their hands, had its origin in this event, being taken up first by the neighbouring nations, and from them communicated to the Greeks and Romans. And it is remarkable that the caduceus of Mercury, the messenger of the gods of Greece and Rome, was formed of two serpents twisted round a rod.