"Before the first day, remove all leaven from your homes." (Shemos
We are forbidden to eat chametz on Pesach. In order to be sure that our
houses are chametz free, we are commanded to clear away and destroy all
chametz on the fourteenth of Nissan, erev Pesach. We also nullify all
chametz that we do not know about in our possession.
The Sages also instituted a search for chametz at the beginning of the
night before Pesach.
The evil inclination is compared to the yeast in the dough, which enables
the dough to rise and become tasty (Berachos 17a). We clear away chametz
to remind ourselves to clear out our arrogance and become more humble, and
also to remind ourselves to avoid over indulging in our desires.