Exodus 10:1-20

10 Then the Lord said to Moses, “Go in to Pharaoh, for I have hardened his heart and the heart of his servants, that I may show these signs of mine among them, 2 and that you may tell in the hearing of your son and of your grandson how I have dealt harshly with the Egyptians and what signs I have done among them, that you may know that I am the Lord.”

3 So Moses and Aaron went in to Pharaoh and said to him, “Thus says the Lord, the God of the Hebrews, ‘How long will you refuse to humble yourself before me? Let my people go, that they may serve me. 4 For if you refuse to let my people go, behold, tomorrow I will bring locusts into your country, 5 and they shall cover the face of the land, so that no one can see the land. And they shall eat what is left to you after the hail, and they shall eat every tree of yours that grows in the field, 6 and they shall fill your houses and the houses of all your servants and of all the Egyptians, as neither your fathers nor your grandfathers have seen, from the day they came on earth to this day.’” Then he turned and went out from Pharaoh.

7 Then Pharaoh's servants said to him, “How long shall this man be a snare to us? Let the men go, that they may serve the Lord their God. Do you not yet understand that Egypt is ruined?” 8 So Moses and Aaron were brought back to Pharaoh. And he said to them, “Go, serve the Lord your God. But which ones are to go?” 9 Moses said, “We will go with our young and our old. We will go with our sons and daughters and with our flocks and herds, for we must hold a feast to the Lord.” 10 But he said to them, “The Lord be with you, if ever I let you and your little ones go! Look, you have some evil purpose in mind. 11 No! Go, the men among you, and serve the Lord, for that is what you are asking.” And they were driven out from Pharaoh's presence.

12 Then the Lord said to Moses, “Stretch out your hand over the land of Egypt for the locusts, so that they may come upon the land of Egypt and eat every plant in the land, all that the hail has left.” 13 So Moses stretched out his staff over the land of Egypt, and the Lord brought an east wind upon the land all that day and all that night. When it was morning, the east wind had brought the locusts. 14 The locusts came up over all the land of Egypt and settled on the whole country of Egypt, such a dense swarm of locusts as had never been before, nor ever will be again. 15 They covered the face of the whole land, so that the land was darkened, and they ate all the plants in the land and all the fruit of the trees that the hail had left. Not a green thing remained, neither tree nor plant of the field, through all the land of Egypt. 16 Then Pharaoh hastily called Moses and Aaron and said, “I have sinned against the Lord your God, and against you. 17 Now therefore, forgive my sin, please, only this once, and plead with the Lord your God only to remove this death from me.” 18 So he went out from Pharaoh and pleaded with the Lord. 19 And the Lord turned the wind into a very strong west wind, which lifted the locusts and drove them into the Red Sea. Not a single locust was left in all the country of Egypt. 20 But the Lord hardened Pharaoh's heart, and he did not let the people of Israel go.

The plagues are like an un-creating of Egypt. The Lord made all things and gave them a proper order and place; the Lord is king and ruler of everything. Pharaoh refuses to recognize the Lord, however, and has arrogated to himself all power and authority. So, the plagues are the Lord’s way of showing Pharaoh that he does not have ultimate authority over the creation. Each plague is an example of what happens when the order of creation is undermined. Here, the insects that have a place in God’s rightly-ordered creation are allowed to upset that order, thereby bringing destruction on Egypt.

I love how Leon Kass puts it:

After each of the first nine plagues, the chaos caused by the Lord he also soon removes: just as each plague is a reversal or undoing of creation, so its removal is a re-creation of the world order. The plagues offer a panorama of “anti-creation,” mocking the attempts of Egypt’s secret arts to alter nature’s workings and revealing both the tragic inner meaning of human attempts to control nature through technology. Such hubristic efforts are ultimately counterproductive: they destroy order, produce chaos, and lead in the end to a world inhospitable to earthly life (think especially of the cattle disease, boils, hail, locusts, and darkness). Clever men can destroy life-sustaining order: only God can create and preserve it. –Leon Kass, from Founding God’s Nation: Reading Exodus

Even Pharaoh’s men are beginning to learn their lesson:

Then Pharaoh's servants said to him, “How long shall this man be a snare to us? Let the men go, that they may serve the Lord their God. Do you not yet understand that Egypt is ruined?” [10:7]

Pharaoh once again temporarily repents, but his true character trumps his repentance and the Lord once again hardens Pharaoh’s heart.