“Moses was…born on the 7th of Adar, which made the month an auspicious one for the Jewish people, not only during the events of Purim but also today.
The Lubavitcher Rebbe points out that a person’s soul shines stronger on his or her birthday. The aspect of the soul that is contained within a person is actually a spark of the person’s root Neshama, which stays above. This Neshama that is above the earthly Neshama is called ‘mazal‘. A person’s mazal is stronger on the birthday because the mazal, which drips vitality into the soul, and the soul are in perfect alignment on that day.
Even though we all individually have birthdays, Moses’s birthday is like the collective birthday of the Jewish people… Because the leader of the Jewish people is equal to the Jewish people collectively (Num. 21:21, Rashi). Since every generation has a spark of the soul of Moses, his birthday is also the birth of the essence of the souls of the Jewish people. This is why the mazal of the Jewish people is stronger in Adar.”