Happiness
The Yidden won the war, and they celebrated on the 14th and 15th of Adar, as it states (9:17-18), ושמחה משתה יום אותו ועשה, "He made it a day of feasting and gladness." These words are written in the singular tense. Why doesn’t the pasuk say, יום אותו ועשו ושמחה משתה, "They made it a day of feasting and gladness," since it was the entire Jewish nation who were celebrating their victory?
The Sfas Emes (Purim ב"תרנ) answers that ועשה refers to Hashem. ושמחה משתה יום אותו ועשה, "Hashem made it a day of feasting and gladness." Chazal tell us that Haman's decree to annihilate Bnei Yisrael ch’v was written and sealed in heaven. Due to their aveiros, Bnei Yisrael deserved this punishment, r'l. But the nation did teshuvah, and Hashem redeemed them. The Sfas Emes explains, משתה יום אותו ועשה ושמחה, Hashem celebrated when the Yidden were saved.
This is because Hashem wants us to annul all harsh decrees, as Chazal say, למנצח ושמח אותו שנוצחין למי, "Hashem is happy when we win Him, and we annul His decrees." The Yidden rejoiced below, and Hashem was rejoicing in heaven. Every year, on Purim, Hashem rejoices and celebrates in heaven. Therefore, we should be happy, too. And if we try to be happy, Hashem will help us succeed.
One year, Reb Yeiva of Ostra’a wanted to be happy on Purim, but it was hard for him, as he was struggling financially. A happy person arrived, they celebrated Purim together, and Reb Yeiva became joyful. Reb Yeiva said that this person was Mordechai HaTzaddik, the baal simchah on Purim. He comes to every Yid to make him happy on Purim.
