Why Matzah?

The first of the 4 Questions on the Seder Night is really.... 
If bread is so problematic on Pesach why do we order pizza the minute after we make Havdalah over beer. And if Matzah is so Holy why should we ever eat leavened bread?!
The Sfas Emes brings together a collage of ideas from Tzadikim to help us understand the deeper meaning of why we eat Matzah on Pesach and why pizza is so holy!