Seven of the ten plagues are described in this week's Torah reading. The purpose of these plagues was, as G-d told Moses: "So that you will be able to tell your children and grandchildren how I have made sport from Egypt, performing miraculous signs there."
Pharaoh is identified with his stubborn boasts, "I do not know G-d," and "the river is mine and I have fashioned it," denying G-d's influence in our world and replacing it with a belief in self and man's power.
The fundamental purpose of the plagues was to negate this approach, to manifest G-dliness openly so that all could see, and in doing so, to break the pride of Pharaoh and his nation.
G-d persisted in this endeavor until "Egypt [knew] that I am G-d," and Pharaoh's pride was crushed. He came to Moses in his nightclothes, entreating G-d's mercy.
And the evidence was not for Pharaoh alone. The miracles of the exodus serve as testimony of G-d's control of the natural order for subsequent generations. In Egypt, even Pharaoh had no choice but to acknowledge G-dliness. At other times, G-d's influence may not be as evident, but it is always He who is ordering our world and our destiny.
Nature itself is no more than a recurring series of miracles. For is there a reason why the sun should rise or the grass should grow?
But beyond the natural order, there is a G-dly hand directing our lives. Nothing happens by chance. Instead, in a way in which only His infinite wisdom can fully comprehend, G-d is guiding our lives and working miracles on our behalf.
This is the message of the miracles of the plagues: to probe beneath the surface and become conscious of G-d's involvement in our lives. The only difference between the plagues in Egypt and our present situation is the degree in which G-d's hand is overtly manifest, but the presence - and the working - of that hand always remains the same.