Pesach is the re-experiencing of the birth and genesis of our nationhood. During the first days, weeks, and even months of a baby’s life the infant cannot eat normal foods. His system is not yet developed and he lacks the ability to chew and digest the foods we eat.
In a similar vein, at the moment of our rebirth we eat matzah, symbolizing that we are nothing in the presence of G-d. It is only after a week of eating matzah and contemplating its vital message that we can reintroduce chometz – representing our own egos – into our diet. It is only when we have been sufficiently reminded that ultimately we are mere pawns in the hands of the Almighty that we can again focus on our pathways of life, and hopefully not lose sight of Who is truly in control of our destiny.
When one brought an offering to the Mishkan/Bais Hamikdash, it was not merely a physical offering of blood or flour. It was meant to be an emotional experience of reconnection and subservience to G-d.
The Netziv (Emek HaDavar) explains that leavened bread represents utilizing human intervention to add to the natural state of creation. When we stand before G-d in His Home, as it were, it is inappropriate it is for us to demonstrate our ability to alter the natural order and manipulate creation. Therefore in the Bais HaMikdash, chometz was virtually never offered on the altar. (The one notable exception was the offering of the Shtei Halechem on Shavuos. On Shavuos, the holiday that celebrates our acceptance of the Torah, we demonstrate that the Torah transcends the natural world. Thus, on that day we demonstrate our greatness, as the adherents to the Torah, even in the Bais Hamikdash.)
For one week of Pesach we rid our homes of chometz and undermine our own egos. In so doing we are reminded not to take ourselves too seriously. It is only when that week is over that we can again enjoy chometz, with an understanding that the essential difference between matzah and chometz is nothing more than hot air.