Midrasch zu Schemot 7:27

See I, etc. (Deuteronomy 11:26): This is what is stated in the verse (Job 36:10-12), "He opens their ear by discipline, etc. If they will listen and serve, they shall spend their days in goodness, their years in delight. But if they will not listen, they shall perish by the sword." "He opens their ear by discipline" - the Holy One, blessed be He, does not bring distress to a person until he opens his ear and warns him, so that he can repent. If he repents, behold, that is good. If not, He brings bad things upon him. From who do you learn [this]? From Pharaoh, king of Egypt. When [God] wanted to bring a plague upon him, he would send and warn him about it through His servant Moshe, as stated (Exodus 10:4), "Tomorrow I will bring locusts on your territory." And so [too], "I will plague your whole country with frogs" (Exodus 7:27). He warns about it "by discipline," [meaning] by the discipline of the Torah. "And he orders them back from wickedness" (Job 36:10), from the cheating people and from cheating to the Holy One, blessed be He. "They shall spend their days in goodness," (Job 36:11) [meaning,] they will complete their years in goodness.

... This is that which is written (Job 36:22), "See, God is beyond reach in His power, who governs like Him?" It is customary in the world that when flesh and blood seeks to do bad to his enemy, he does so immediately so that [the other] not become aware. But the Holy One, blessed be He, warns Pharaoh about each and every plague, so that he would repent. This is that which is written (7:17), "In this you will know that I am the Lord"; (7:27) "behold I will plague all of your borders with frogs"; (9:19) "send, hasten your cattle."

And the Lord said unto Moses: “Rise up early in the morning, and stand before Pharaoh; lo, he cometh from the water” (Exod. 8:16). Why did Pharaoh go to the waters early in the morning? Because the wicked one boasted that since he was a god, he had no need to go to the water to relieve himself. Therefore he went out early in the morning so that no one would see him performing a demeaning act. That is why the Holy One, blessed be He, said to Moses: Rise up early in the morning, when he must (go out), and say unto him: Thus saith the Lord, the God of the Hebrews … for I will this time send all My plagues upon thy person, etc. (Exod. 9:14). Ordinarily, when a man desires to harm his enemy, he does so unexpectedly lest he be forewarned, but the Holy One, blessed be He, warned the wicked Pharaoh before each plague, as it is said: Behold, I will cause it to rain (ibid., v. 18), Behold, tomorrow will I bring locusts into thy border (ibid. 10:5). And He did so in each instance.