Q. Why do we keep Purim in the second month of Adar in a leap year?
Both are festivals of redemption and linking Purim to Pesach gave the day greater credibility at a stage when the rabbis were taking their time (Meg. 7a) before agreeing to include the Book of Esther in the Hebrew Bible.
Their major problem was that the book nowhere mentions the name of God. In this context it is relevant to quote Rabbi SM Lehrman in his Guide to Hanukkah and Purim:
“A sense of Divine Providence pervades all the dramatis personae, especially the hero Mordecai and the heroine Esther. In fact, if the Book possesses any slogan, it is this: ‘The Guardian of Israel neither slumbereth nor sleepeth’ (Psalm 121:4)”.