The matzah is an important part of the seder, because it represents the Jews exit of Egypt and the rush that they were in. They were trying to exit Egypt, and they were making bread, but it didn't rise, and they were in a rush to leave, so that pharaoh didn't change his mind and not let them leave. The bread turned into matzah, and that is why we eat matzah.

haggadah Section: Motzi-Matzah