The Gemara in Masechet Ta’anit (29a) tells us, “Rabbi Yehuda son of Rav Shmuel ben Shilat taught in the name of Rav: Just as when the month of Av begins happiness is diminished, so too, when Adar begins happiness increases. Rav Papa says, therefore, if a Jew has a court case with a gentile pending, he should avoid having it in the month of Av when the Jewish nation’s fortune is bad, and try to have it held during the month of Adar when the Jewish nation’s fortune is good.”
The source for this is based on a verse in Megillat Esther which states, “And the month which was switched for them from tragedy to joy,” which teaches us that the good fortune of this month brings about salvation and goodness for Israel, for indeed their fortune is very good during this month.
The commentaries ask: How can the Gemara say that during the month of Adar the fortune of the Jewish people is good, does the Gemara (Shabbat 156b) not say that the Jewish nation has no fortune, which means that they are not under the influence of various stars and constellations as are the other nations of the world, rather they under the direct supervision of Hashem? There are several answers to this question.
The Ritba (Rabbeinu Yom Tov ben Avraham) writes that although the Jewish nation has no fortune, in the months of Av and Adar they are indeed under the influence of the constellations, for this was the way it was decreed by Hashem. He adds that it is possible that the Jewish nation is never under the influence of the constellations and what is meant by the Gemara that Adar is auspicious etc. is that during the month of Adar, good things are decreed upon the Jewish people. (These decrees are directly from Hashem, blessed is He, and not from the constellations or stars for the Jewish nation is not influenced by them.)
The Maharsha explains that what our Sages meant when they said that “the Jewish nation has no fortune” is that if it was decreed in Heaven that no punishment befall Israel or that a certain good thing happen to them, it will surely happen as such, regardless of any stars or constellations. However, if, G-d forbid, something bad was decreed on a specific person, it will usually befall him during times when his fortune is not the best. Thus, many tragic experiences have befallen the Jewish nation during the month of Av and especially on Tisha Be’av (the Ninth of Av). Similarly, when good things are decreed upon a specific person, they will usually befall him when his fortune is good and the month of Adar is especially auspicious for the Jewish people.
However, Hagaon Chatam Sofer writes that this law that a Jew who has a pending court case with a gentile should try to have it fall out during the month of Adar, is halachically incorrect. His reasoning for this is because the Jewish nation has no fortune. It is for this reason that the Rambam omits this Halacha from his great work, for the Halacha is that one should not pay any attention to these matters, as Israel has no fortune. Maran Harav Shlit”a disagrees with this opinion, for it is quite clear from the words of the aforementioned authorities that although the Jewish nation has no fortune, nevertheless, it is still possible that during the month of Adar their overall fortune is better. We can explain that the reason why the Rambam omits this law from his work is because this matter is not of halachic nature; rather it is only a wise piece of advice.