From here on, we begin our Torah study of the redemption of the Jewish people from Egypt. This week's parashah mentions seven of the ten plagues that God sent to deliver the people from slavery.
Why did God decide to send plagues upon Egypt? If we were to say it was to punish the Egyptian people for making the Jews suffer, it would be difficult to understand why the punishment had to take the form of miraculous and strange plagues. God has many ways to punish; He could have destroyed them in an instant instead of making them suffer for months, and He could have used various miracles.
To understand the answer, we must analyze the situation more closely. Pharaoh's first reaction when Moses asked him to free the Jewish people was to ask, "Who is God, that I should listen to him?""
The Egyptians did not believe in HaShem. That is why God punished them through supernatural plagues, in order to teach them the greatness of God.