Why does God harden Pharaoh's heart?

וַיֹּ֣אמֶר יְהֹוָה֮ אֶל־מֹשֶׁה֒ בְּלֶכְתְּךָ֙ לָשׁ֣וּב מִצְרַ֔יְמָה רְאֵ֗ה כׇּל־הַמֹּֽפְתִים֙ אֲשֶׁר־שַׂ֣מְתִּי בְיָדֶ֔ךָ וַעֲשִׂיתָ֖ם לִפְנֵ֣י פַרְעֹ֑ה וַאֲנִי֙ אֲחַזֵּ֣ק אֶת־לִבּ֔וֹ וְלֹ֥א יְשַׁלַּ֖ח אֶת־הָעָֽם׃

Exodus 4:21

And יהוה said to Moses, “When you return to Egypt, see that you perform before Pharaoh all the marvels that I have put within your power. I, however, will stiffen his heart so that he will not let the people go.

אבן עזרא על שמות ד׳:כ״א:א׳

ויאמר. זה אמר לו במדין והנה הודיעו כי השם יחזק את לבו ולא ישלחם בעבור כל המופתים שיראם עם המופת האחרון:

Ibn Ezra on Exodus 4:21:1

AND THE LORD SAID. This was told to Moses in Midian. God informed Moses that He would harden Pharaoh’s heart and that Pharaoh would not let them go despite all of the wonders, including the last one, that He would show them.

God made Pharaoh stubborn and unwilling to let the Israelites go free from slavery. This was part of a plan to show God's power through miracles and eventually free the Israelites. Interpretations may differ on why this happened, some focusing on God's purpose and others on human choice.

The idea of God hardening Pharaoh's heart suggests that God allowed or intensified Pharaoh's existing stubbornness rather than directly changing his heart. This was part of God's plan to demonstrate His power through miraculous events and ultimately free the Jews from slavery. The concept acknowledges Pharaoh's free will and portrays God's involvement as working within the context of Pharaoh's disposition to fulfill a broader divine purpose. Different interpretations exist, but the common theme is that God's role is more about permitting the natural course of events in line with His plan.