פּירוש אויף שמות 10:1

ויאמר ה' אל משה בא אל פרעה AND THE LORD SAID UNTO MOSES GO IN UNTO PHARAOH and warn him.

בא אל פרעה כי אני הכבדתי את לבו ואת לב עבדיו, “go toPharaoh for I have hardened both his heart and that of his servants;” We have not found this formulation in connection with any of the previous plagues. The reason that G-d reacted so harshly was that after Pharaoh himself had confessed that he had sinned, instead of releasing the Israelites, both he and his servants continued to oppress the Israelites. This retraction by Pharaoh forced G-d’s hand, so to speak, to react in kind, matching the punishment to the sin committed. [In verse 34 at the end of the last chapter the Torah testified that Pharaoh’s servants had supported him in his retraction of his confession. Ed.]

בוא אל פרעה....מביא מחר, “go in unto Pharaoh...I will bring on the plague of locusts tomorrow to your territories.” How had Moses had advance warning of this plague, seeing that we have no word in the Torah where G–d had given him advance notice about this plague? We will have to fall back on the tradition that the acronyms of the ten plagues as per Rabbi Yehudah, had been etched into the side of his staff. The problem with this interpretation is that if so why did G–d bother to give him advance notice of the two plagues following after the plague of locusts? It may be more plausible to assume that the words למען תספר באזני בנך ובן בנך את אשר התעללתי במצרים, “in order that you will be able to tell your son and your grandson what I have wrought upon Egypt,” (verse 2) that this had included details about the forthcoming plague of locusts. We find that the plague of locusts recorded in the Book of Yoel (Yoel 1,3-4) was also introduced by the prophet telling his people to tell his children and grandchildren about it. [In that instance the plague of locusts smote the land of Israel. Ed.]