Commentary for Exodus 14:8

ויחזק ה׳ את לב פרעה AND THE LORD ALLOWED THE HEART OF PHARAOH TO BE HARDENED — the meaning is, that he was in doubt whether to pursue or not, and He hardened his heart to pursue (Mekhilta d'Rabbi Yishmael 14:8:1).

ובני ישראל יוצאים ביד רמה, the meaning of the word רמה here is similar to the meaning of the same word in Deuteronomy 32,27 ידינו רמה, where it means: “our own hand has prevailed.” At the time of their departure they had been confident of their ability to defeat Pharaoh and his military machine as they were much stronger in numbers. The verse teaches that they were relying on their numbers instead of considering their total lack of experience in the art of war. They would have had every reason to fear the numerically inferior Egyptians who had all this experience going for them.

ויחזק ה׳ את לב פרעה, G'd hardened the heart of Pharaoh, etc. The Torah means that G'd needed to harden the heart of Pharaoh otherwise he would not have had the courage to face a nation which had recently left Egypt with their heads held high. The various considerations we described above were part of this process the Torah describes as "G'd hardened the heart of Pharaoh."