BS”D
In parshas Shemos, HaShem for the first time informs Moshe Rabbeinu that He will strengthen Pharaoh’s heart, and Pharaoh will repeatedly refuse to release the Jewish people from Egypt:
The Lord said to Moses, “When you go to return to Egypt,
see all the signs that I have placed in your hand
and perform them before Pharaoh, but I will strengthen his heart,
and he will not send out the people.”
וַיֹּאמֶר יְהֹוָה אֶל משֶׁה בְּלֶכְתְּךָ לָשׁוּב מִצְרַיְמָה רְאֵה כָּל הַמֹּפְתִים אֲשֶׁר שַׂמְתִּי בְיָדֶךָ
וַעֲשִׂיתָם לִפְנֵי פַרְעֹה וַאֲנִי אֲחַזֵּק אֶת לִבּוֹ וְלֹא יְשַׁלַּח אֶת הָעָם:
(Shemos 4:21)
This same concept appears several times throughout Sefer Shemos (for example, Shemos 7:3 and 10:20).
Chazal grapple with the question of how the strengthening and hardening of Pharaoh’s heart by HaShem goes together with the concept of free will. Moreover, how can HaShem even punish Pharaoh for his stubborn refusal to release the Jewish people if he was not acting on his own?
“Does this not provide heretics with ground for arguing
that he had no means of repenting,
since it says: ‘for I have hardened his heart’?
(Midrash Rabbah, Shemos 13:3)
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Pharaoh Was Always Given a Choice
One explanation is that Pharaoh’s free will was not compromised at all; in fact, it was enhanced. Chazal tell us that Pharaoh initially fought to hardened his own heart during the first five plagues so he would not give in and accept HaShem’s sovereignty. Only then did HaShem step in to further strengthen Pharaoh’s resolve as the plagues increased in intensity (Midrash Rabbah, Shemos 13:3). A close reading of the Torah text involving the plagues further confirms this explanation.
The truth is it was the plagues themselves which impaired Pharaoh’s ability to make a free will decision to accept HaShem or reject Him. Had HaShem not hardened Pharaoh’s heart, Pharaoh would likely have released the Jews due to the intense pain, suffering, and fear that the plagues inspired. This would not have been a free will decision on the part of Pharaoh, nor would it have had any connection to true teshuva. At some point during the remaining five plagues, the decision to release the Jews would then have been forced upon him, so to speak.
In order to give Pharaoh the choice to either accept or reject God, his heart had to be strengthened to withstand the intensity of the plagues (See Seforno on Shemos 7:3).
For this reason, the midrash later states, “I will harden his heart … to exact retribution from them” (Midrash Rabbah, Exodus 5:7). To his detriment, Pharaoh used his Divinely influenced inner strength to merely continue his stubborn refusal to accept HaShem. Pharaoh and his nation were thus deserving of the fullest degree of Divine punishment.
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HaShem Strengthens the Heart
HaShem’s influence over Pharaoh tells us a lot about the concept of free will. At each and every moment, we all 
have the choice to either come closer to HaShem or pull ourselves away. This applies even when we are faced with the biggest, hardest, and most frightening life experiences- whether those experiences are external or they stem from our own inner world. Moreover, this applies regardless of how the person has acted in the past.
הֶחָפֹץ אֶחְפֹּץ מוֹת רָשָׁע, נְאֻם אֲדֹנָי יְהוִה: הֲלוֹא בְּשׁוּבוֹ מִדְּרָכָיו, וְחָיָה
“Do I strongly desire the death of the wicked person?” Says HaShem.
Is it not rather [that I seek] his return from his ways that he may live?”
(Yechezkel 18:23)
At the same time, we can also learn an important lesson from Pharaoh about the path to inner strength and resiliency in the face of difficult yissurim. HaShem will never send someone a challenge that he can’t withstand.
אין הקב“ה בא בטרחות עם בריותיו לא בא על האדם אלא לפי כחו
“HaShem does not bring [unnecessary] difficulties to His creations;
He only brings upon a person that which is according to his ability [to handle].
(Midrash Rabbah, Shemos 34:1)
This means, even when the situation at hand becomes exceedingly difficult, we have the potential to receive the Divine Assistance to not only withstand it, but to achieve real growth and ultimately come closer to HaShem because of it.
In Sefer Tehillim, we read:
קַוֵּה, אֶל–יְהוָה: חֲזַק, וְיַאֲמֵץ לִבֶּךָ; וְקַוֵּה, אֶל–יְהוָה
Hope to HaShem, be strong,
and He will put courage in your heart [literally: make your heart strong],
and [you will thereby] hope to HaShem [at an even greater level].
Tehillim 27:14
In the Gemara it says:
“R. Hama son of R. Hanina said: If a man sees that he prays
and is not answered, he should pray again, as it says,
‘Hope to HaShem, [but if the first hopeful prayer doesn’t help]
be strong, and He will put courage in your heart, and [you will thereby]
hope to HaShem [at an even greater level].
(Gemara, Brochos 32b)
By actively fighting to have emunah in HaShem in a time of darkness and doing what you can to maintain that emunah, HaShem will respond by strengthening your heart so that you will not be overwhelmed and overcome by your troubles. Instead, you will be endowed with an inner strength to carry on, and you will be free to make the choice to take your emunah to an even higher level. You will thus be deserving of the fullest degree of Divine reward- both in this world and the next.
