One of the issues you will face while reading Exodus is the hardening of Pharaoh.
In Exodus 4:21, God introduces the theme when He says:
And the LORD said to Moses, “When you go back to Egypt, see that you do before Pharaoh all the miracles that I have put in your power. But I will harden his heart, so that he will not let the people go.” (Exodus 4:21, ESV)
Mark Dever provides the following help on this verse:
Sometimes people say, “Okay, God hardened Pharaoh’s heat in the sense that he allowed Pharaoh to harden his own heart.” I appreciate the attraction of that interpretation; it is not lost on me. Yet I want to point out that this is not what the text says. I don’t claim to understand everything about how God hardened Pharaoh’s heart, or all of its implications. But the verse certainly says that God had a purpose in hardening Pharaoh’s heart. Further, 4:21 appears to be the controlling verse for what follows in the rest of the story. This is the first time the matter is mentioned. And many more statements about Pharaoh’s hard heart follow during the plagues in chapters 7-11. Some say that the Lord hardens Pharaoh’s heart (7:3-5; 9:12; 10:20,27; 11:10). Some simply report that his heart became or was hard (7:13-14, 22; 8:19; 9:7). And some state that Pharaoh hardens his own heart (8:15, 32). All three kinds of descriptions are used at the end of chapter 9 and the beginning of chapter 10, and the text is clear: right after the plague of hail and before the plague of locusts, Pharaoh hardens his heart and is described as sinfully culpable; yet God concludes the matter by describing himself as the ultimate cause:
When Pharaoh saw that the rain and hail and thunder had stopped, he sinned again: He and his officials hardened their hearts. So Pharaoh’s heart was hard and he would not let the Israelites go, just as the LORD had said through Moses.
Then the LORD said to Moses, “God to Pharaoh, for I have hardened his heart and the hearts of his officials.” (9:34-10:1a)
Source: Mark Dever, Promises Made, p.92