Why did g_d harden Pharaoh's heart?

Question

Why did g_d harden Pharaoh's heart when he had to get the Israelites free later?

did he want to show them that he is the almighty omniscient or something else?

Answer 1

There are a few key verses.

First Shemot (Ex.) 3:19 - G-d tells Moses, "I know that Pharoah won't allow you to leave unless I show him my strong hand." It seems a given that unless he was shown G-d's might, Pharoah was in full control of things. So, he had to be "punished" in some way. But, of course, it doesn't directly address why G-d hardens his heart to do this job (showing G-d's might). BTW, look at Shemot 5:2 where Pharaoh asks who is this "adon-ai" that I should listen to him? So, it's clear that G-d had to show him something.

In Shemot 7:3 G-d says that he will harden Pharaoh's heart so that he can increase his wonders in Egypt.

Rash"i explains that G-d determined that it had already been reveled that he would not do teshuva from his evil ways. Therefore, it is appropriate that he hardens Pharaoh's heart so that he would understand my strength. He states that G-d's method is to bring punishments on the idolatrous nations of the world in order that Israel observe and fear G-d (and not imitate this behavior.)

Siftei Chachamim expands on this concept further. He says that G-d says that if I didn't harden his heart and just brought about the plagues, people might think that G-d punishes people who do teshuva. But I (g-d) know that he won't repent with a full heart. Therefore, I have to harden his heart so that others will understand the reason for the plagues that follow. Note that Siftei Chachamim tries to explain Rashi's explanation on G-d's method also because the verse implies that G-d wants to increase the punishments beyond the measure of the actual sin. See the source.

Answer 2

There are several different points that are made in the various answers.

1. Pharaoh at first hardened his own heart in order to withstand the earlier plagues. Once he had established the pattern, Hashem allowed him to continue in that pattern by hardening later to be able to resist the later plagues.

2. Hashem only strengthened Pharaoh so that he could make an independent decision at all times. That is, He was trying to allow Pharaoh to do the right thing of his own free will. Pharaoh refused to take advantage of that opportunity.

3. Pharaoh, by consistently refusing to send them out of his own free will, forfeited the ability to choose as the final punishment had been decreed. Once he reached that level of evil, he could not turn back.

See what I answer at What does it mean that God hardened Pharaoh’s heart?.

There are a number of answers ranging from strengthening Pharaoh so that he could withstand the plagues, to the difference in language showing that Pharaoh hardened his own heart at first and G0d only did that later after Pharaoh had reached the level of requiring punishment, ...

Check out Hardened Hearts: Some Explanations to see some of them Reinterpretation of the Term (Saadiah Gaon), The Modest Solution (Ramban), The Bold Claim: Pharaoh Acts Freely (Albo), Hardening as Punishment (Rambam)

Pharaoh's Heart goes into detail on the theme of Pharaoh having reached a level through his own free will in which this was an appropriate punishment.

An interesting point is that the word for 'harden' is actually 'heavy'. The Egyptian superstition was that when being judged after death, a person's heart was weighed against a feather (the feather of Truth IIRC). If the heart was lighter, he was judged innocent. Thus, Pharaoh hardening his own heart can mean that he was guilty even in terms of his own beliefs. Hashem hardening his heart can therefore mean that Pharaoh is now punished by those means or that his refusal (in his own terms) to repent causes him to lose the ability to repent, or by moving along the path of error he has that much farther to go to return, ...

Rav Shimshon Rafael Hirsch prefers the idea that Hashem helped strengthen Pharaoh so that he had free will and could make a totally objective decision. He prefers the meaning to be 'strengthen' rather than 'harden'.

Also note @Fred giving the pointers

Also, for some examples of articles that discuss some of the major views among the rishonim on this, see here, here, here, and here