“Matza symbolizes self-negation before G-d. It is flat, showing that we are nothing without Him. Chametz, on the other hand, symbolizes our independent contribution, where G-d wanted us to use our free will to contribute to His world and bring His Presence into it. Chametz can of course get out of hand and turn into arrogance if a person loses track of where his independence came from and what he should do with it. But independence in itself is a necessary and desirable part of our religious life.
“On Pesach G-d reveals Himself to us with great mercy and redeems us from Egypt. Our reaction: matza. We negate ourselves to Him and just say thank you. We are totally in the receiving mode. The only tactful response to this great Chesed is to say thank you and realize how powerless we are without Him. However, we eventually wait for the chance to, so to speak, give something back to G-d. That chance comes on Shavuot, when we offer the chametz sacrifice of the two breads, the ‘shtei halechem.’ This is our personal contribution to G-d’s world, the not overly puffed up chametz. We realize that anything we have to offer is thanks to Him, for Him, and according to His Torah (that he gave us on Shavuot). But it is our way of showing ‘hakarat hatov,’ appreciation.”