Midrasch zu Schemot 7:10

And Aaron forthwith cast down his rod before Pharaoh and before his servants, and it became a serpent (Exod. 7:10). Whereupon Pharaoh said: “Is this the full power of your God? Why, my magicians travel throughout the world performing such feats.” Then Pharaoh called also (ibid., v. 11) the youths, and babes of five, yea, even of four years, and each of them cast his rod. It is written: Pharaoh called also because he disdained at first to summon his magicians and sorcerers. Our sages of blessed memory said: He actually performed a great miracle with that rod. When one serpent is able to swallow other serpents, that is not unusual, but this serpent turned itself back into a rod again, as it is written: But Aaron’s rod swallowed up their rods (ibid., v. 12). If a man made bundles out of the rods that were cast to the ground to become serpents, there would have been more than ten bundles, yet Aaron’s rod swallowed them all and it became no larger than it was previously. When Pharaoh beheld that, he was amazed and exclaimed: “Surely if he should command the rod to swallow Pharaoh and his throne, it could swallow them.” That was the sign that He had given to Moses at the bush when He said: This which is in thy hand, cast it to the earth (ibid. 4:2). The word this alludes to Pharaoh, who is compared to a snake, as is said: The Lord with His sore and great and strong sword will punish leviathan the slant serpent (Isa. 27:1). When Moses withdrew from Pharaoh’s presence, the wicked one said: “If this son of Amram comes near me again, I will slay him, I will hang him, I will burn him.” That is why, when Moses returned, Pharaoh became like a rod. And Pharaoh’s heart was hardened, and he harkened not unto them, as the Lord had spoken (Exod. 7:13). With reference to the first five plagues, the words Pharaoh’s heart was hardened, etc., are written, but after the fifth plague occurred and he still would not permit them to leave, the Holy One, blessed be He, said: Henceforth, even if he desires to send them away, I will not allow it. Hence, with reference to the last five plagues it is written: But the Lord hardened Pharaoh’s heart (ibid. 10:20). Moses decreed what was to transpire, and the Holy One, blessed be He, executed it, as it is said:: Thou shalt also decree a thing, and it shall be established unto thee (Job 22:28).

5.

(Exod. 7:10:) SO MOSES AND AARON CAME… It was proper for Aaron to enter first because he was three years older than < Moses >, but in the eyes of the Egyptians Moses was greater, as stated (in Exod. 11:3): {AND} ALSO THE MAN MOSES WAS VERY GREAT IN THE LAND OF EGYPT….