On the night of the Seder, we have an obligation to view ourselves as if we left Mitzrayim. This is no small task and many commentators have questioned how it is possible. We have to seriously arouse our emotions for this, and the Seder provides a night filled with emotional stimuli to help.
At the center of these stimuli is the Matzah, a simple food of just flour and water. But it is around this food that we need to do emotional gymnastics. We have to think of Matzah as the staple we ate when we were slaves in Egypt. And at the same time, this is the food that we baked in haste as we left Mitzrayim.
Matzah is to be transformed in our minds and our hearts from slave rations to the food of freedom. Perhaps Hashem is showing us that we can control our thoughts, and through our mind we can control our emotions. The whole night we are being trained to go from thoughts of slavery to thoughts of freedom so that we can actually come to feel that we ourselves, each one of us, actually left Mitzrayim and thank Hashem with all our hearts.
I think that I saw a comment somewhere to the effect that the Gra viewed Matzah as the bridge between slavery and freedom because of this very paradoxical fact that the slave food served as the first food for the newly freed Jewish people.