I heard this dívar Torah from my
dad who heard it from Rabbi Zucker.
It would seem that according to the Rambam, on Chanukah, if you didnít make a Shehechieonu on the first night on the candles, you donít make Shehechieonu the second night. But on Purim if you didnít make Shehechieonu the first night on the Megilah, you can make it the next day? What is the difference between the days?
We say Shehechieonu on the persumay nisa, or publicizing the miracle. The way to publicize the miracle on Purim was instituted differently by Chazal than the publicizing the miracle on Chanukah. The way to publicize the miracle on Purim is reading the Megilah. And reading the Megilah is publicizing the miracle per se. The lighting of the candles on Chanukah is not a publicizing of the miracle per se. There are a number of reasons why you would light candles at night. The real publicizing of the miracle is the day of the twenty fifth of Kislev. The Gemarah says that on the twenty-fifth of Kislev there are eight days of Chanukah. So we see that the first day of Chanukah is the main day therefore the publicizing of the miracle is tied to that day. Therefore if you forget to make a Shehechieonu on the first day of Chanukah you cannot say it on the second day. You have lost the day of the 25th. You cannot get that back. But on Purim, since the publicizing of the miracle is the reading of the Megilah, if you didnít say Shehechieonu the first night, you can make it the next day. You can still fulfill the reading and hence the mitzvah of publicizing the miracle.
How come Chazal instituted two types of publications? There are two ways the Jews can be saved, by repenting or by the special relationship between the Jews and God. So on Purim we were saved by repentance but by, Chanukah we were saved by the special relationship with us and God.
On Purim since we were saved by repenting, Chazal instituted that we commemorate with an action of reading the Megilah. On Chanukah no repenting took place, so we commemorate with the day.