The Sanctity of Purim
Rabbi Samuel Abba of Slovita said: "There is a saying that when other memorable days are no longer observed, Purim will still be commemorated. This means that all our festivals are demonstrations of God's miracles, but Purim is in commemoration of a natural event. Though we may not merit it that God deliver us in a miraculous manner, nevertheless we may still hope for aid in a natural way."
Source: Hasidic Anthology