Tefillos Accepted After the Decree is Sealed:
The Bais Avrohom of Slonim zy”a quotes the Berditchover Rebbe zy”a as saying that the miracle of Purim proved to us that even after a decree is signed and sealed, we can annul it through tefillah and teshuva. The gates to Heaven can always be opened to accept our prayers and teshuva, and Hashem will always receive them and provide us with salvation.
Tefillos for Luxuries:
The pasuk states (Esther 9:12): “What is your request and I will give it to you, and what do you ask for additionally, and I will do it.”
My grandfather, the Kreitchnifer Rebbe zy”a, explains that the word “additionally” (od) is reference to “mosros” (luxuries), which a person wants but does not really need to survive. Usually, it is difficult to ask Hashem for such things. However, on the day of Purim all gates of Heaven are open to our prayers and one can even ask Him for luxuries.
The Evil forces Have No Power on This Day:
The pasuk states (Esther 7:6): “And Haman became terrified“. Sefer Sifsei Tzadik writes that this refers to all forces of impurity. On this day, they all are terrified and fearful. Therefore, this is a good time to daven for whatever we need.
The Gemara says (Rosh Hashanah 16B) that we blow the shofar in order to confuse the satan. So too, the satan is confused and worried on Purim, which allows our tefillos to be heard and accepted on this day.
