The culmination of days of frenzied pre-Pesach cleaning is bedikat chametz. After days or weeks of sweeping, searching and scouring, designed to remove anything that looks or tastes like bread or other leavened food from our homes, bedikat chametz is the final check.
On the night before Pesach, we go around the house armed with a candle, a feather and a dustpan, searching the nooks and crevices to make sure that we have not missed any crumbs. The idea of searching with a candle is that its light penetrates better into dark places. Some people have the custom of putting out pieces of bread beforehand to make sure that they actually find something. (This practice makes me nervous. We want to make more crumbs! On erev Pesach!)
Searching for chametz enables us to fulfil two key commandments related to Pesach: that there be no chametz in our homes and that we see no chametz. Many, especially Chasidic, commentators have also seen a metaphorical spiritual dimension in the search. Chametz is identified with puffed-up pride, personal grandiosity and self-deception. Bedikat chametz also requires us to search our souls and spring clean for these traits.