On Pesach, we are mekabel ol malchus Shamayim--we accept the yoke of Hashem as king upon ourselves. We have left Mitzrayim, and are no longer under the jurisdiction of a kingdom who wishes to prevent us from serving Hashem. Our acceptance of Hashem as king is not a once in a year obligation--rather, we fulfill it every day when we recite krias shema. Every day, we renew our commitment, just as every day, Hashem renews the world. This koach (power) of hischadshus (renewal) is the power of the yetzer tov, and gives the strength and vitality to renew our commitment to Hashem, especially accessed on the night of the Seder.