A friend of mine who has been reading a great deal of John Calvin's Institutes said something to me a couple months ago which has been resonating within me ever since. At this point (as of today, that is) I'm beginning to think that what my friend had to say--thanks, in part, to Calvin--is probably closer to the truth than what I believed previously.
What did my friend say? I'm glad you asked that! He said, and I paraphrase:
Unfortunately, many Christians tend to bandy about the words "free will," as if we are somehow on the same level as God in this regard. Now no one would likely even suggest she or he were on the same level as God, but does not attributing "free will" to human beings, simply because they are created in the image of God, imply that? Perhaps a far better expression than "free will" would be "the ability to choose." Now I can live with that!
Having talked with my friend just today, I think he is saying that God has not given an absolutely free will to those He created in His image; rather, He has given them the ability to choose, or to make choices. Only God's will is truly free.
God can do, say, or think virtually anything and everything He wants to do, say, or think. I say virtually, of course, because God cannot lie, He cannot be unfaithful to His holy word and His promises, and most significantly, He cannot think, say, or do anything which is not in keeping with His holy and perfect will, Being, and character. (Oh, and no, He cannot create a rock which is too heavy even for Him to lift, because God does not even entertain a single, solitary, illogical thought, let alone engage in illogical behavior.)
Of the scores of Bible passages I could quote in support of my last paragraph, I will quote but one, and that is 2 Timothy 2:13 NAS:
"[Even] if we are faithless, He remains faithful, for He cannot deny Himself."
Put differently, God cannot be anything but what He is, and He is perfection personified. The heavenly hosts realize this truth, and that is why they worship God ceaselessly, and will continue doing so through all eternity. Furthermore, God is immutable, unchangeable, and His holiness assures us of His unchangeableness. In this regard, the hymn writer caught some of the transcendence of God when he wrote,
"Immortal, invisible, God only wise,
In light inaccessible, hid from our eyes.
Most blessèd, most glorious, the Ancient of Days,
Almighty, victorious, Thy great name we praise. (words by Walter C. Smith, 1824-1908)
All this to say, there are times when God intervenes in the affairs of mere mortals, and for His own purposes and according to His own sovereign will does things which both surprise and mystify us. After all, He alone is God. We are not. God told Isaiah,
"'For my thoughts are not your thoughts,
Nor are your ways My ways,' declares the LORD.
'For as the heavens are higher than the earth,
So are my ways higher than your ways,
And my thoughts than your thoughts'" (55:8-9).
This is not to say, however, that God, as in the account of the hard-hearted Pharaoh of Moses' day, completely bypassed Pharaoh's will. God's will simply trumped Pharaoh's will in the matter. Pharaoh was free to choose to ignore God's word through Moses, but only because it was God's will for Him to do so. Only God's will is free; Pharaoh's will, on the other hand, was constrained and hemmed in by God's sovereign will. Then too, the hardening by God of Pharaoh's heart was at least in part because Pharaoh hardened his heart first. That is at least something to think about.
Does this mean we are not free to choose whether we harden our hearts or not? No, but it does mean our choosing takes place within a larger context; namely, God's ultimate (aka decretive, sovereign, or hidden) will. As one author put it, and I paraphrase for perhaps better clarity,
This understanding of [God's] sovereign will does not imply that God causes everything to happen. Rather, it acknowledges that because He is sovereign, He . . . permits or allows whatever happens to happen. This aspect of God’s will acknowledges that even when God passively--seemingly, to us--permits things to happen, He . . . [in fact] chooses to permit them, because He always has the power and right to intervene. God can always decide either to permit or stop the . . . events of this world. Therefore, [only] in the sense He allows things to happen, has He . . . [willed them to happen] . . ..
God, in other words, can intervene at any time and at His discretion. In doing so, He neither obviates our wills nor makes us choose to do His will; rather, His decretive will trumps our finite human wills. In Jeremiah 18 we read,
"'Arise and go down to the potter's house, and there I will announce My words to you.'
Then I went down to the potter's house, and there he was, making something on the wheel.
But the vessel that he was making of clay was spoiled in the hand of the potter; so he remade it into another vessel, as it pleased the potter to make. 'Can I not, O house of Israel, deal with you as this potter does?' declares the LORD. 'Behold, like the clay in the potter's hand, so are you in My hand, O house of Israel'"(vv.2-6).
Apostle Paul mirrors these words in Romans chapter 9, which apropos your question includes a section on God's dealings with Pharaoh:
What shall we say then ? There is no injustice with God, is there? May it never be! For He says to Moses, "I WILL HAVE MERCY ON WHOM I HAVE MERCY, AND I WILL HAVE COMPASSION ON WHOM I HAVE COMPASSION." So then it does not depend on the man who wills or the man who runs, but on God who has mercy. For the Scripture says to Pharaoh, "FOR THIS VERY PURPOSE I RAISED YOU UP, TO DEMONSTRATE MY POWER IN YOU, AND THAT MY NAME MIGHT BE PROCLAIMED THROUGHOUT THE WHOLE EARTH." So then He has mercy on whom He desires, and He hardens whom He desires. You will say to me then, "Why does He still find fault ? For who resists His will ?" On the contrary, who are you, O man, who answers back to God ? The thing molded will not say to the molder, "Why did you make me like this," will it? Or does not the potter have a right over the clay, to make from the same lump one vessel for honorable use and another for common use?
The key verses, above, would seem to be verses 18-20, which I paraphrase as follows:
God chooses either to have mercy upon or to harden whomever He wills. If we say to God, "Well, how can you blame Pharaoh for hardening his heart if You are the One who hardened it? Evidently, no one can resist your will!" By saying that, you miss the point. Who are you, a mere lump of clay in the Master Potter's hands, to question His ways and say "You can't do that, God!"? What hubris!
There is no contest between God's will and ours. God's will always trumps ours, because He will sovereignly bring to pass the plans He formulated within the Godhead from eternity, before time existed. As Paul said in Ephesians, chapter 1:
". . . we [have] been predestinated according to His purpose, who works all things after the counsel of His will" (part of v.11)
In His sovereign will God gives us the ability to choose to obey or choose not to obey His revealed will, whether it be delivered to a stubborn and proud Pharaoh through Aaron and Moses, or to an average Joe or Jill today through His written word, the Scriptures.
In conclusion, until the end of time, I imagine, God's image bearers will never cease trying to reconcile two seemingly irreconcilable, yet inevitably true, biblical statements. I put forward only two such statements:
"'Come unto me, all ye that labour and are heavy laden, and I will give you rest. Take my yoke upon you, and learn of me; for I am meek and lowly in heart: and ye shall find rest unto your souls. For my yoke is easy, and my burden is light'" (Matthew 11:29-30 KJV).
"'No one can come to Me unless the Father who sent Me draws him; and I will raise him up on the last day'" (John 6:44 NASB Updated Version).
What other two seemingly irreconcilable biblical statements can you come up with? I leave it to you.