The Talmud on the Redemption of Purim and the Redemption of Passover

The Talmud explains that the redemption represented by Purim was not complete. True, the Jews were saved from annihilation plotted by Haman, but they still remained subject to Ahasuerus (B. Meg. 14a), whereas the redemption commemorated by Pesach (Passover) they ceased to be subjects to Pharaoh ... During a leap year, it is the usual practice to all the things that must be done during the month of Adar during First Adar, in conformity with the principle that 'one must not pass by precepts' (B. Pes. 64b). Purim, however is celebrated only during Second Adar (M. Meg. 1:4). The Talmud suggests that since Purim and Pesach both celebrate the deliverance of Israel, they should occur close to one another (Levush. O.H. 697).[Isaac Klein, A Guide to Jewish Services]