Shem Mishmuel: Vaeira III
In Parsha Va’eira we learn about the first 7 plagues and the hardening of Pharoh’s heart. Sefer Shemos, Parsha Va’eira, Perek 7, posukim 3-5 state, “I will harden Pharoh’s heart, and I will multiply My signs and My wonders in the land of Egypt. And Pharoh will not listen, and I will set my hand against Egypt. I will take out … My people, the B’nai Yisrael, from … Egypt with great judgement. And Egypt will know that I am Hashem when I raise my hand against Egypt, and I will bring out the B’nai Yisrael from among them.” Shem Mishmuel writes that it is clear that the Exodus didn’t require these 10 plagues.
Once Pharoh refused the first request to allow Klal Yisrael to leave, Hashem could simply have flattened and annihilated Egypt with one mighty blow. But this would not have achieved the main purpose of the Exodus, not the destruction of Egypt, but a demonstration of Divine power which left no room for doubt that Hashem controls the world. The more miracles wrought in Egypt, the greater and clearer the realization that Hashem, the G’d of Israel, was in charge of His world. (Sefer Shem Mishmuel, Parsha Va’eira, page 119). This concept was borne out in Yithro’s reaction to the miracles performed by Hashem on behalf of Klal Yisrael; “Now I know that Hashem is greater than any other deity…”
In short, the plagues and Pharoh’s feigned “teshuva” after each followed by the “hardening of Pharoh’s heart” was orchestrated by Hashem as a means of bringing forth many more Divine wonders in order to bring about teshuva amongst the Egyptians, to show both B’nai Yisrael and the other nations who is truly in charge of the world and to mold, unify and solidify Klal Yisrael as a Nation which cleaves to Hashem.