The first time that Moses made his application to Pharaoh, he produced his instructions only; now he is directed to produce his credentials, and does accordingly. 1. It is taken for granted that Pharaoh would challenge these demandants to work a miracle, that, by a performance evidently above the power of nature, they might prove their commission from the God of nature. Pharaoh will say, Show a miracle; not with any desire to be convinced, but with the hope that none will be wrought, and then he would have some colour for his infidelity. 2. Orders are therefore given to turn the rod into a serpent, according to the instructions, Exo 4:3. The same rod that was to give the signal of the other miracles is now itself the subject of a miracle, to put a reputation upon it. Aaron cast his rod to the ground, and instantly it became a serpent, Exo 7:10. This was proper, not only to affect Pharaoh with wonder, but to strike a terror upon him. Serpents are hurtful dreadful animals; the very sight of one, thus miraculously produced, might have softened his heart into a fear of that God by whose power it was produced. This first miracle, though it was not a plague, yet amounted to the threatening of a plague. If it made not Pharaoh feel, it made him fear; and this is God's method of dealing with sinners - he comes upon them gradually. 3. This miracle, though too plain to be denied, is enervated, and the conviction of it taken off, by the magicians' imitation of it, Exo 7:11, Exo 7:12. Moses had been originally instructed in the learning of the Egyptians, and was suspected to have improved himself in magical arts in his long retirement; the magicians are therefore sent for, to vie with him. And some think those of that profession had a particular spite against the Hebrews ever since Joseph put them all to shame, by interpreting a dream which they could make nothing of, in remembrance of which slur put on their predecessors these magicians withstood Moses, as it is explained, Ti2 3:8. Their rods became serpents, real serpents; some think, by the power of God, beyond their intention or expectation, for the hardening of Pharaoh's heart; others think, by the power of evil angels, artfully substituting serpents in the room of the rods, God permitting the delusion to be wrought for wise and holy ends, that those might believe a lie who received not the truth: and herein the Lord was righteous. Yet this might have helped to frighten Pharaoh into a compliance with the demands of Moses, that he might be freed from these dreadful unaccountable phenomena, with which he saw himself on all sides surrounded. But to the seed of the serpent these serpents were no amazement. Note, God suffers the lying spirit to do strange things, that the faith of some may be tried and manifested (Deu 13:3; Co1 11:19), that the infidelity of others may be confirmed, and that he who is filthy may be filthy still, Co2 4:4. 4. Yet, in this contest, Moses plainly gains the victory. The serpent which Aaron's rod was turned into swallowed up the others, which was sufficient to have convinced Pharaoh on which side the right lay. Note, Great is the truth, and will prevail. The cause of God will undoubtedly triumph at last over all competition and contradiction, and will reign alone, Dan 2:44. But Pharaoh was not wrought upon by this. The magicians having produced serpents, he had this to say, that the case between them and Moses was disputable; and the very appearance of an opposition to truth, and the least head made against it, serve those for a justification of their infidelity who are prejudiced against the light and love of it.

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.

When Pharaoh shall speak unto you, saying, show a miracle for you,.... To prove that they came from God, the Jehovah they said they did, and that they were his ambassadors, and came in his name, and made the demand for him; which when he seriously reflected on things, he would be ready to require, hoping they would not be able to show any, and then he should have somewhat against them, and treat them as impostors:

then thou shalt say unto Aaron, take thy rod; the same that Moses had in his hand at Horeb, and brought with him to Egypt; this he had delivered into the hand of Aaron, who was to be his agent, and with this rod do signs and wonders as he did, and on account of them it is sometimes called the rod of God:

and cast it before Pharaoh, and it shall become a serpent; as it became one before at Horeb, when Moses by the order of God cast it on the ground, and afterwards became a rod again, as it now was, Exo 4:2 Hence Mercury, the messenger of the gods with the Heathens, is represented as having a "caduceus", a rod or wand twisted about with snakes (p).

(p) Vid. Chartar. de Imag. Deorum, p. 136. imag. 48.

When Pharaoh shall speak unto you, &c.--The king would naturally demand some evidence of their having been sent from God; and as he would expect the ministers of his own gods to do the same works, the contest, in the nature of the case, would be one of miracles. Notice has already been taken of the rod of Moses (Exo 4:2), but rods were carried also by all nobles and official persons in the court of Pharaoh. It was an Egyptian custom, and the rods were symbols of authority or rank. Hence God commanded His servants to use a rod.