According to the Halacha (Shulchan Aruch Orach Chaim 695:4), each Jew is required to send two foods to at least one other Jew on Purim.
The Peleh Yo’Eitz notes that the best way to perform the mitzva is for a great person to give to a lesser member of society. This would create both joy and the potential for one mitzva to lead to others.
After all, as the Sfas Emes emphasizes, one of the intents behind this mitzva is to debunk Haman’s slander (Esther 3:8) that Jews are splintered. Besides, acts of chesed are the foundational groundwork for the rebuilding of the Beis HaMikdash (bimheira biyameinu).
Perhaps this is one reason for the Talmudic opinion (Megillah 7b) that one could also fulfill one’s obligation of mishloach manos by sending Torah.
Interestingly, Rav Shlomo Alkabetz wrote the oft-quoted M’nos HaLevi as a mishloach manos gift to his in-laws.
In Eparyon, Rav Ganzfried, author of the Kitzur Shulchan Aruch, considers mishloach manos as a cunning way to give charity. Since all people will be giving gifts to their friends, the poor would not feel embarrassed by accepting a handout. This also explains why the order of the mitzvos listed in this verse seems out of order, with the more important mitzva of tzedaka being mentioned last.
The Sha’arey Simcha writes that the reason for this order is that it is debatable which miracle was greater: the destruction of our enemies or the raising of the Jews. Therefore, there are two mitzvos, paralleling each of these miracles, respectively.
The Ohel Moshe notes that, as opposed to other Holy Days, where the mitzvos of the day (i.e. lulav, matza, shofar, etc.) are only relevant for those days, Purim’s mitzvos (i.e. tzedakah, chesed, learning Megillas Esther, etc.) are relevant all year long.
R’ Meir Yechiel of Ostrovtza says that the implication of the word “re’eyhu” (“his fellow”) is that every Jews is considered worthy of receiving mishloach manos on Purim in H-Shem’s Eyes.
The Chasam Sofer was asked if mishloach manos are Halachically for increasing unity or to help all Jews have the minimal means with which to celebrate. If it is for unity, then it is for the benefit of the giver; if it is to allow everyone to celebrate, it is for the receiver. A practical difference would be in a case where someone refuses to accept. In such a case, has the sender fulfilled one’s obligation? If it is for the giver, the answer is yes, whereas if it is for the receiver, the answer is no.
Once, when about to receive mishloach manos, the Brisker Rav looked outside to check if it was yet sunset, and thus no longer Purim. He was willing to accept mishloach manos for purposes of the mitzva, but was unwilling to accept it as a regular gift, in fulfillment of the words of the wisest of men (Mishlei 15:27) that one “who hates gifts lives.”
Regarding the unique language of this verse, the Ben Ish Chai notes that the gematria of manos (“gifts”) (40+50+6+400=496) is the same as the 50 cubits of Haman’s gallows with the word maves (“death”) (40+6+400=446), meaning that this mitzva is intended to remind us of Haman’s plan to kill Mordechai.
The Talmud (Megillah 5b) explains each of the different expressions for this holiday to mean a different method for celebrating the day. Simcha (“joy”) is interpreted as not giving eulogies (in the event of a death); v’mishteh (“and feasting”) is interpreted as prohibiting fasting; and v’yom tov (“and the holiday”) is interpreted as prohibiting work on Purim. Later, the Talmud (Megillah 7a) interprets the phrase mishloach manos (“sending gifts”) as the requirement to send through a messenger at least two kinds of food to at least one friend.
The Rambam (Mishneh Torah, Hilchos Megillah 2:15) writes that even two poor people are required to send another poor person some food to fulfill their obligations.
The Trumas HaDeshen writes that the exchange of food is intended to make sure everyone has enough for the feast.
M’nos HaLevi writes that we send gifts to promote friendship because achdus (“unity”) rescued the Jews.
The Midrash HaGadol on Devarim points out that this demonstrates the greatness of chesed because we were rescued because of it.
Ginzei HaMelech writes that we use a messenger because this shows achdus (“unity”) in requiring another person to get involved in this mitzva. Similarly, he points out, this is why Megillas Esther always uses Yehudim for Jews, since the root of that word is echad, one. Furthermore, the giving of gifts through messengers acts as an additional tikkun for Yaakov’s giving gifts (Bireishis 32:14-17) to Eisav, the ancestor of Amalek, through messengers.
The Vilna Gaon and Midrash Shmuel note that the Jews’ celebrating in this way parallels the three parts of Haman’s plan (Esther 3:13); the joy serves to counteract Haman’s plan to destroy the Jews, the feasting serves to counteract Haman’s plan to kill the Jews, and the Yom Tov serves to counteract Haman’s plan to annihilate the Jews.
The Vilna Gaon writes that, eventually, Purim was not accepted as a full Yom Tov because that would keep people from performing the other mitzvos of Purim.