Chometz (leaven) symbolizes kelipa (separation from holiness). That is why we keep our distance from even the tiniest amount of chometz, just as a person takes every possible precaution to protect himself from robbers who wish to take his life.
While getting rid of all the chometz, we should have in mind our desire that just as we are scrubbing and scouring away even the minutest amount of chometz, HaShem should destroy every last bit of the yetzer hora (the evil inclination) from the world. We are certain that HaShem, Who sees all the work the Yidden invest in cleaning for Pesach, will do away with the kelipa and the golus we are in.
All the work we do for Pesach must be carried out with love and simcha, with no room for anger and arguments. And the money which which we buy the Yom-Tov necessities should be honestly earned. Otherwise, one would be feeding the kelipa with kedusha.
(ספר קב הישר פרק פ”ט)
via Lma’an Yishme’u.