Thank you for your question on God hardening Pharaoh’s heart, “Why do Exodus 4:21 and Exodus 7: 3 say that God hardened Pharaoh’s heart?”
The reason for God hardening the heart of Pharaoh’s heart is a difficult question to answer.
I would like to suggest for one’s consideration that Pharaoh ALREADY hardened his own heart or conscience before God spoke to Moses. Here are some things for one’s pondering:
A. Pharaoh hardened his own conscience when he enslaved the Hebrew people without any real cause. It was fear that drove him to enslave them. The Hebrew people had no shown any disloyalty to Pharaoh.
Exodus 1 says this, “He said to his people, “Behold, the people of the sons of Israel are more and mightier than we. 10 Come, let us deal wisely with them, or else they will multiply and in the event of war, they will also join themselves to those who hate us, and fight against us and depart from the land.” 11 So they appointed taskmasters over them to afflict them with hard labor. And they built for Pharaoh storage cities, Pithom and Raamses. 12 But the more they afflicted them, the more they multiplied and the more they spread out, so that they were in dread of the sons of Israel. 13 The Egyptians compelled the sons of Israel to labor rigorously; 14 and they made their lives bitter with hard labor in mortar and bricks and at all kinds of labor in the field, all their labors which they rigorously imposed on them” (A searchable online Bible in over 150 versions and 50 languages). Bible citations are in the New International Version.
Pharaoh saw the injustice and hard labor that he placed on the Hebrew people. He began searing his own conscience when the slaves cried for mercy before Pharaoh.
B. Pharaoh hardened his own heart when he ordered the midwives to kill the sons that were born to the slaves. Certainly Pharaoh knew that this action was wrong to ask the midwives to kill the baby boys that were born. The midwives had more conscience than Pharaoh.
Exodus 1 says this, “Then the king of Egypt spoke to the Hebrew midwives, one of whom was named Shiphrah and the other was named Puah; 16 and he said, “When you are helping the Hebrew women to give birth and see them upon the birthstool, if it is a son, then you shall put him to death; but if it is a daughter, then she shall live.” 17 But the midwives feared God, and did not do as the king of Egypt had commanded them, but let the boys live. 18 So the king of Egypt called for the midwives and said to them, “Why have you done this thing, and let the boys live?” 19 The midwives said to Pharaoh, “Because the Hebrew women are not as the Egyptian women; for they are vigorous and give birth before the midwife can get to them” (NIV).
C. Pharaoh and the Egyptians hardened their own hearts when Pharaoh every Egyptian to throw any baby boy infant into the Nile River. The Egyptians knew that was wrong for they wouldn’t their own sons be killed and yet they obeyed Pharaoh’s command.
Exodus 1 says this, “Then Pharaoh commanded all his people, saying, “Every son who is born you are to cast into the Nile, and every daughter you are to keep alive” (NIV).
Did Pharaoh hardened his conscience in his actions against the enslaved Hebrews? One may or may not agree with my thought that Pharaoh did hardened his own heart first. Would Pharaoh let the enslaved Hebrews free? I don’t believe so for they were his source of labor. Who would serve in his courts and fields and the homes and pastures of the Egyptians? It was the enslaved Hebrews. His fear that if he let them go would still haunt him for then they might join an invading army to have revenge on Egypt. It was a risk that he was not willing to accept to let the enslaved Hebrews go.
As one reads the narrative account, God does hardened Pharaoh’s heart after 8 plagues fell on Egypt. Pharaoh “repented” but changed his own mind each time. In the 7 previous plagues, Pharaoh’s heart was self-hardened. God confirmed Pharaoh’s hardened heart or hardened his heart, but in either case Pharaoh had hardened his own heart before the 8th plague.
Would it be so unjust for God to hardened Pharaoh’s heart for what he has done to his people? Would Pharaoh free the enslaved Hebrews on his own? Pharaoh was the mightiest ruler in his part of the world. He was not going to bow to the God of the Hebrews or to Moses. His pride and position were at stake.
SUMMARY: God hardened Pharaoh’s heart because his heart was already hardened by his cruel actions toward the enslaved Hebrews. God was going to reward him, repay him back for what Pharaoh did to his people.
For more perspectives:
https://www.quora.com/Why-do-Exodus-4-21-and-Exodus-7-3-say-that-God-hardened-Pharaohs-heart