“…From when Adar arrives, joy is increased…” – Talmud, Taanis 29a

משנכנס אדר מרבין בשמחה – תענית כט,א

The month of Adar is a season of joy and good fortune. For this reason, our Sages taught that if one has a court case against a gentile, he should try to schedule the trial for the month of Adar, as the entire month is a favorable time for the Jewish people (Taanis, ibid.)

The start of the celebration from the beginning of the month, “from when Adar arrives,” seems somewhat premature. After all, the victory over our enemies in the Purim story took place only on the 13^th of the month, meaning that for the first 12 days of Adar the Jews were still at great risk of being decimated! On the other hand, the permission for the Jews to defend themselves was already granted nine months earlier, so the start of Adar marked no significant change in their status. From where does the Talmud deduce that the entire month of Adar is a time to be joyous and a season of good fortune?

There is, however, another great event that we know impacted the entire month of Adar—the birth of Moshe. The Talmud (Megillah 13b) relates that when Haman was drawing lots to determine a date for his plot to annihilate the Jews, he rejoiced when the lot fell on the month of Adar, saying, “The lot has fallen for me on the month in which Moshe died.” What Haman did not know, concludes the Talmud exultantly, was that Moshe was also born in the month of Adar.

(Moshe’s birth in Adar also explains Rashi’s enigmatic comments on the above passage in the Talmud. Rashi writes, “From when Adar arrives: they were miraculous days for the Jewish people, Purim and Pesach.” Rashi’s unusual reference to the holiday of Pesach, which is not in Adar but in Nissan, as a cause for celebration in Adar, alludes to the birth of Moshe,  in Adar, whose leadership of the Jewish people in the exodus from Egypt we commemorate on Pesach.)

We thus see that the birth of Moshe on the 7^th of Adar produced not one series of miracles, but two. Moshe’s birth brought about not only the redemption from Egypt, which he led, but the miraculous salvation of the Jews in the story of Purim as well, due simply to the “chance” occurrence of Haman’s plot in the month in which Moshe was born. This propensity for miracles, brought about by Moshe’s birth on the 7^th of Adar, is what makes every single day of the month a reason to celebrate.

—Likkutei Sichos, vol. 16, pp. 345-347