"That they should make them days of feasting and joy, and of sending portions one to another, and gifts to the poor." (9:22)
The Rambam in Hilchot Megillah (2:17) writes: "It is better to increase in gifts to the poor than in sending portions to one another." If so, why in the pasuk is sending portions to one another mentioned before gifts to the poor?
When giving tzedakah to the poor, it is very important that one should be extremely careful not to embarrass the recipient. (See Rambam, Matanot Aniyim 10.)
When Mordechai instituted Purim as a day of giving gifts to the poor, he was greatly concerned lest it become known as the poor's day to receive handouts. Therefore, he also instituted the exchanging of portions among friends so that an observer would be unable to distinguish gifts to the poor from gifts to friends. To conceal the gifts to the poor, the Megillah preceded it with sending portions to one another.
With the above-mentioned we can understand why no berachah is made over the mitzvah of mishlo'ach manot -- sending portions to one another.
The Rashba (responsa 18) writes that when one performs the mitzvah of tzedakah, he does not make a berachah - because possibly the person will refuse to accept. According to Ramah (Orach Chaim 615:4), when one sends portions on Purim, he fulfills the mitzvah of mishlo'ach monot even if the recipient refuses them.
Consequently, if a berachah would be made over mishlo'ach manot and not matanot le'evyonim, it would be obvious what is mishlo'ach manot and what is matanot le'evyonim, thus defeating the entire purpose of instituting mishlo'ach manot.
"They should make them days of feasting and joy, and of sending portions one to another, and gifts to the poor." (9:22)
Why did Mordechai institute this as a way to celebrate the miracle of Purim?
Haman complained to Achashveirosh about the Jewish people that though they were only one nation among many nations, they were "mefuzar umeforad bein ha'amim" -- in total disharmony among themselves. They lacked love and compassion for their fellow Jews. To counteract this claim, Esther said to Mordechai, "Go gather together all the Jews" (4:16), and stress to them the importance of unity and Ahavat Yisrael.
Since the decree was caused by Haman's allegation that there was disunity among the Jewish people, Mordechai instituted that on Purim we exchange edibles with friends and give gifts to the poor to demonstrate our love for one another.
"Therefore they called these days 'Purim' because of the Pur (the Lot)." (9:26)
"Purim" is the plural for pur. Why isn't the yom tov called "Pur"?
In order to be sure that the day determined by the 'lot' was indeed correct, Haman made two lots. In one box he placed 13 pieces of paper, each containing one of the Hebrew months of the year (the miracle of Purim took place in a leap year, see Talmud Yerushalmi Megillah 1:5, P'nei Moshe). In the other box he put 385 pieces of paper, each containing a number from 1 to 385, for all the days of the year. Haman thought as follows: If from the first box he pulled the month of Sivan (the third month) and from the second box he pulled the number 200, then something would be wrong, since the 200th day of the year cannot occur in the third month.
Haman was satisfied when he pulled Adar Sheini (the thirteenth month) from the first box, and 368 from the second, because this came out to be the 13th day of Adar Sheini, and obviously the two lots supported each other. Hence, the yom tov is known as "Purim," because of the two lots.