God instructs Moses to inform the Israelites about the Covenant, and the upcoming Exodus, but because of the troubles they have had with the Egyptians because of Moses, they do not care to listen to Moses. So God tells Moses to speak to Pharaoh about letting the Israelites go. Included in the plan is the idea that Pharaoh will resist (because God will interfere with his judgment and harden his heart), which will allow God to present a number of gruesome miracles to the Egyptians. The intention was to sear into the consciousness and memory of the Egyptians the power of God. To me, this smacks of the tribalism of the cruder aspect of the God of the Torah, that He favors the Israelites at the expense of the other nations, and that outsiders are outside of His mercy. It also smacks of the revenge fantasies of an oppressed people.
In an audience with Pharaoh, Aaron throws down his staff, and it turns into a viper. Pharaoh's court sorcerers throw down their staves which also turn to vipers, but Aaron's viper devours the other vipers before turning back into a staff of the same thickness as before. This does not impress Pharaoh.
This sets into motion a series of ten plagues God wreaks upon the Egyptians. God has Moses tell Aaron to strike the Nile with his staff, causing the water to turn into blood. This causes all water in Egypt to turn into blood, even the water in wells and cisterns. All the fish in the Nile died of the pollution. Because Pharaoh's sorcerers also could turn water into blood, Pharaoh was not impressed.
After a week of this, God tells Moses to ask Pharaoh again to release the Israelites, threatening an infestation of frogs. Pharaoh refuses, and frogs appear everywhere, and annoy the Egyptians. This annoys Pharaoh, even though his court sorcerers can also summon frogs. Pharaoh summons Moses and Aaron, and asks them to beg God to remove the frogs, promising the release of the Israelites and a big sacrifice to God if He will remove the frogs. God relents and the frogs all die, leaving stinky frog corpses throughout Egypt. The people clear the stinky frog corpses away, and Pharaoh reneges on his promise.
God next sends a plague of lice, which swarm and annoy the Egyptians. Pharaoh's sorcerers cannot reproduce the trick, and the lice bite all the animals and humans in Egypt. Pharaoh's sorcerers warn him that this is the finger of God making this happen. Pharaoh refuses to relent.
The next plague is a plague of arov (עָרֹב), the translation of which is in dispute. In the Midrash, Rabbi Nechemia thinks they are flies, but Rabbi Yehuda thinks they are a mixture of wild animals. More of the later Torah commentators regard them as wild animals. The King James Bible has them as swarms of flies. For the first time, the arov will attack only the Egyptians and not the Israelites.
Pharaoh partially relents, and allows the Israelites to sacrifice to God in Egypt, but Moses holds out for a full release. Moses refuses. Pharaoh then allows the Israelites to travel for three days into the desert to sacrifice to God, as long as they pray for Pharaoh as well. But as soon as Moses prays the creatures away, Pharaoh hardens his own heart, and reneges on his promise.
The next plague is that of livestock: horses, cattle, sheep, donkeys and camels in the possession of the Egyptians all die. But none of the Israelites' livestock are affected. But this did not move Pharaoh to release the Israelites.
The next plague is a plague of boils. Moses throws a handful of furnace soot into the air before Pharaoh, and it lands and causes boils on the flesh of the animals and people wherever it lands. The court sorcerers are affected so badly by this that they cannot appear in court to refute Moses and Aaron. This time, God forces Pharaoh to be obstinate, and he refuses to let the Israelites go. God tells Moses to tell Pharaoh that the only reason God hasn't killed off the Egyptians yet is because he wants survivors to remain who can tell the story of God's power.
The next plague is a plague of brutal hail, hailstones so big that they can kill whoever goes outside, man or beast. The hailstones kill every human and animal who is outside when they fall. They smash every tree, and destroy all the crops. The hail does not fall on the Israelites. Pharaoh relents.
And Pharaoh sent, and called for Moses and Aaron, and said unto them, I have sinned this time: the LORD is righteous, and I and my people are wicked. Entreat the LORD (for it is enough) that there be no more mighty thunderings and hail; and I will let you go, and ye shall stay no longer. [Exodus 9: 27-28].But as soon as Moses prays the hail away, Pharaoh hardened his heart, and would not let the Israelites go, just as God had predicted.
What are we to make of this? To modern sensibilities, this seems protracted and cruel. And yet, we remember this story to this day because of the number and magnitude of these plagues. From our viewpoint, we know that Israel is released, the Egyptian army is drowned in the Red Sea, and the Hebrews return to the Promised Land and eventually form a kingdom there. These plagues build momentum for the exodus to follow.