The hardening of Pharaoh's heart is a significant theme in the narrative of the Exodus, where God delivers the Israelites from Egyptian bondage. This theme is primarily found in the Book of Exodus, where it is mentioned multiple times in the context of the plagues that God sends upon Egypt. The hardening of Pharaoh's heart serves as a demonstration of God's sovereignty and power over human will and the forces of nature.

Biblical References:

1. Initial Hardening:
The first mention of Pharaoh's heart being hardened occurs in Exodus 4:21, where God instructs Moses: "When you return to Egypt, see that you perform before Pharaoh all the wonders I have given you the power to do. But I will harden his heart so that he will not let the people go" . This sets the stage for the subsequent confrontations between Moses and Pharaoh.

2. Pharaoh's Own Hardening:
In several instances, the text indicates that Pharaoh himself hardened his heart. For example, after the plague of frogs, Exodus 8:15 states, "But when Pharaoh saw that there was relief, he hardened his heart and would not listen to them, just as the LORD had said" . This suggests a willful resistance on Pharaoh's part to God's commands.

3. Divine Hardening:
The narrative also emphasizes that God actively hardens Pharaoh's heart. In Exodus 9:12, it is written, "But the LORD hardened Pharaoh’s heart, and he would not listen to them, just as the LORD had told Moses" . This divine action underscores the fulfillment of God's purposes and the demonstration of His power.

4. Purpose of Hardening:
The hardening of Pharaoh's heart serves a dual purpose. It allows God to display His might through the plagues and ultimately leads to the liberation of the Israelites. In Exodus 10:1-2, God explains to Moses, "Go to Pharaoh, for I have hardened his heart and the hearts of his officials so that I may perform these signs of Mine among them, and that you may tell your children and grandchildren how I dealt harshly with the Egyptians and how I performed My signs among them, and that you may know that I am the LORD" .

5. Final Hardening:
The culmination of this theme is seen in the final plague, the death of the firstborn, after which Pharaoh finally relents and allows the Israelites to leave. However, even after this, God hardens Pharaoh's heart once more, leading to the pursuit of the Israelites and the eventual destruction of the Egyptian army in the Red Sea (Exodus 14:4-8).

Theological Implications:

The hardening of Pharaoh's heart raises important theological questions about free will, divine sovereignty, and human responsibility. From a conservative Christian perspective, this narrative illustrates God's ultimate authority and His ability to use even the resistance of human leaders to accomplish His divine purposes. It also serves as a warning against the dangers of hardening one's heart against God's will, highlighting the importance of obedience and submission to God's commands.

Throughout the Exodus account, the hardening of Pharaoh's heart is a testament to God's power and a pivotal element in the unfolding of His redemptive plan for His people.