“When Adar enters,” the Talmud declares, “we increase in joy.” For this is “the month that was transformed for them from sorrow to joy, from mourning to festivity” (Esther 9:22) by the great miracle and victory of Purim. Our sages advise that the month of Adar is an auspicious time for the Jewish people, so that if a Jew is faced with a challenging event (i.e., a court case, a medical procedure, etc.) he should endeavor to schedule it during Adar.
The Tanya: Explained 