When Pharaoh shall speak unto you, saying, Shew a miracle for you: then thou shalt say unto Aaron, Take thy rod, and cast it before Pharaoh, and it shall become a serpent. Show a miracle for you - A miracle, מופת mopheth, signifies an effect produced in nature which is opposed to its laws, or such as its powers are inadequate to produce. As Moses and Aaron professed to have a Divine mission, and to come to Pharaoh on the most extraordinary occasion, making a most singular and unprecedented demand, it was natural to suppose, if Pharaoh should even give them an audience, that he would require them to give him some proof by an extraordinary sign that their pretensions to such a Divine mission were well founded and incontestable. For it appears to have ever been the sense of mankind, that he who has a Divine mission to effect some extraordinary purpose can give a supernatural proof that he has got this extraordinary commission.
Take thy rod - This rod, whether a common staff, an ensign of office, or a shepherd's crook, was now consecrated for the purpose of working miracles; and is indifferently called the rod of God, the rod of Moses, and the rod of Aaron. God gave it the miraculous power, and Moses and Aaron used it indifferently.