http://revach.net/article.php?id=1986

Section: Moadim   Category: Purim
Purim: Alshich HaKadosh - Moshe Rabbeinu and Matanos L'Evyonim

Why do we give Matanos L'Evyonim on Purim? The Alshich HaKadosh says in the name of the Ralbag that after Gezeiras Haman, Eliyahu went to Moshe and asked him to daven to Hashem to spare the Yehudim. Moshe Rabbeinu asked Eliyahu if there was a tzaddik down on earth who can help him with his tefilos. Eliyahu answered that there is tzaddik named Mordechai. Moshe told Eliyahu to tell Mordechai to daven and Moshe would daven at the same time. Hopefully between the two of them there would be a Geula.

In appreciation for Moshe Rabbeinu's help in bringing the Yeshua, Mordechai HaTzaddik instituted Matanos L"Evyonim in order that each person should give tzedoka on Purim L'Zecher Nishmas Moshe Rabbeinu.