The difference between bread and matzah is that between being and nullification of being.
Matzah is the saltless and yeastless simplicity of the bread substance, without size or taste.
It is as though the King of Kings had appeared to halt the dough in its becoming, keeping it at its humblest, lowest possible state (of human nourishment).
We are enjoined to eat matzah for all the seven days of Pesach–"Matzot shall feed the seven days."
This rather surprising formulation may be explained by realizing that what is meant are the seven lower attributes:
Hesed, Gevurah, Tiferet, Netzah, Hod, Yesod, and Malkhut.
The love from the highest feeds the life of the lower.
For He renews, in His Goodness, the act of Creation each day,
–Rabbi Adin Steinsaltz
From The Candle of God by Rabbi Adin Steinsaltz