It can't be coincidence that all the Mitzvot of Purim start with a Mem: Megila (reading); Mishloach Manot (that's a double!); Matanot L'evyonim; Mishteh (the Purim Seuda) and Machatzit Ha-Shekel (giving 1/2 shekels in remembrance of the gifts to the Bet HaMikdash). What is going on here?

To answer, we must look into the mystic meaning of the Mem and why that letter is so connected to Purim. There are 2 forms of the Mem - the regular Mem is open, and the final Mem is closed (the only one of the 5 final letters that is closed). The Gemara (Shabbat 104) explains that the open Mem represents the revealed Torah and the closed Mem represents the Torah’s secrets. This is essentially the story of Purim: All the events in the Megila happen in a revealed manner, but they are guided by Hashem in a hidden fashion. That is why G-d's name is not mentioned in the Megila, and that is why Hadassa is called Esther (hidden). Water - mayim - begins & ends with Mem; when you look at the sea, you see the water, but the amount of land beneath it is hidden from view. So the Torah is compared to water, because so much of its wisdom is hidden beneath the surface. Mem is also the first letter of Moshiach, & the last letter of "rechem" - womb. Just as the womb "hides" the child to be born, so Moshiach exists in every generation, but will only be revealed when we merit it. The avid acceptance of the Mitzvot at the end of the Megila ("kimu v'kiblu ha-Yehudim") is the surest way to bring Moshiach.