On the evening prior to Passover, Rabbi Schneur Zalman of Liadi said to his disciples: "Soon we shall search for chametz—as the Mishna instructs: ‘On the eve of the fourteenth of Nissan, by the light of a candle’ we must search all ‘recesses and crevices’ of our homes for chametz.
"Searching for chametz involves more than removing every particle of physical leaven from our domain; it also means eradicating every last vestige of spiritual leaven—self-inflating pride—from every ‘recess and crevice’ of the fourteen elements of our personality: the seven character traits of one’s ‘animal self’ and the seven character traits of one’s ‘G‑dly self.’
"This, too, is a search to be conducted ‘by the light of a candle’—by the light of one’s ‘Candle of G‑d,’ the soul of man."
On the thirteenth of Nissan of that year, Rabbi Schneur Zalman was so preoccupied with his preparations for the search for chametz that he ate nothing the entire day (he did not fast—it is forbidden to fast during the month of Nissan—he just didn’t eat). The search took all night, though Rabbi Schneur Zalman and his wife lived in a single room at the time.
"My father once told me: ‘Yosef Yitzchak—during the seder, concentrate on becoming a mensch, and G‑d will help. Especially when the door is opened for Elijah—don’t pray for the physical, pray for the spiritual.’" (Rabbi Yosef Yitzchak of Lubavitch.)