Then the LORD said to Moses: Tell the Israelites to turn back and camp in front of Pi-hahiroth, between Migdol and the sea, in front of Baal-zephon; you shall camp opposite it, by the sea. Pharaoh will say of the Israelites, ‘They are wandering aimlessly in the land; the wilderness has closed in on them.’ I will harden Pharaoh’s heart, and he will pursue them, so that I will gain glory for myself over Pharaoh and all his army; and the Egyptians shall know that I am the LORD. And they did so.
When the king of Egypt was told that the people had fled, the minds of Pharaoh and his officials were changed toward the people, and they said, “What have we done, letting Israel leave our service?” So he had his chariot made ready, and took his army with him; he took six hundred picked chariots and all the other chariots of Egypt with officers over all of them. The LORD hardened the heart of Pharaoh king of Egypt and he pursued the Israelites, who were going out boldly. The Egyptians pursued them, all Pharaoh’s horses and chariots, his chariot drivers and his army; they overtook them camped by the sea, by Pi-hahiroth, in front of Baal-zephon. (Exodus 14:1-9)
All’s fair in love and war. And God’s conflict with Egypt was both. With the death of the first born, Pharaoh finally relented and gave in to Moses and Moses’ God, letting the people at last do what they have been asking for: he granted them his permission to take three days off from work to go somewhere to sacrifice to their God, together with all their children and wives and all their livestock. He couldn’t keep fighting; Egypt was a mess, people were dead; for the best of the nation, he had to let the slave’s God have his way.
But then, after the three days had passed, when the slaves stayed gone and it became clear that they were making a break for freedom, Pharaoh had to act. He’d been suspicious all along that Moses had in mind something more than just a worship service of singing, praying and animal sacrifice. He’d been suspicious of the requirement that the people go as whole families, leaving nothing and no one behind. Pharaoh had lied over and over to Moses, but he now saw that Moses had been lying to him just as much. So, Pharaoh had no choice: he couldn’t let Moses steal all his property. He had to run and get it all back. So he sent his army off to track down the runaway slaves and return them to where they had come from. Plagues or not, he wasn’t ready to see all his property gone. He hadn’t suffered enough yet to lose the slaves for good.
Once again, Pharaoh underestimated God. He had lost his farms, his wealthy, and now he was about to lose his power: his army would be wiped out. Human strength would be weakness compared to God.