The month which was transformed for them from sorrow to joy..
Book of Esther 9:22

When the month Adar enters, increase in joy
Talmud, Taanis 29.

Yet Adar’s is no “ordinary” joy. More than the joy derived from a fortunate event, more than the delight in a pleasing break in the monotonous ordinary, it is the joy of transformation. It is the joy of the bitter turned sweet, of the adverse converted into a positive force.

The transformative nature of Adar joy is also reflected by the context in which the Talmud proclaims it the most joyous of months. The statement quoted above does not appear in the tractate of Megilah, where the Talmud elaborates on the miraculous events of Purim and set down the laws and costumes of the merry festival. Rather, it appears in the tractate Taanis (“fasts”) in the midst of a discussion of the most tragic date in the Jewish calendar. On the 9th of Av, we fast and mourn the destruction of the Holy Temple. “When the month of Av enters, decrease in joy,” states the Talmud; then in its commentary of this law, it mentions: “but when Adar enters, increase in joy...”

Once every two or three years Adar doubles in size. This is due to the unique structure of the Jewish calendar: since the Jewish year is comprised of 12 lunar months, it averages only 354 days (12x29.5). To bring it in sync with the seasons of the 365.25-day solar year, a leap year of 13 months is scheduled seven times in a 19-year cycle. The added month is an Adar II, making the leap year Adar (including its Rosh Chodesh days) a 60-day affair.

“Sixty” is a number which figures prominently in the Torah’s dietary laws (the Kosher laws). If a non-kosher (“impure”) foodstuff is dissolved in or cooked together with kosher food, the entire lot is rendered unfit for consumption. However, if the “negative influence” amounts to 1/60th or less of the total mass, it is “nullified by sixty.” The “impure substance” is neutralized and, furthermore, becomes part and parcel of the kosher whole.

  Of all months, Adar is the only one to double it to sixty. For Adar is the month of joyous transformation, the month with the “nullifying power” of sixty. The power to transform an undesirable — even destructive — force into a nourishing joy and delight.