The month that was reversed for them from grief to joy. -Esther 9:22

When the month of Adar enters, we increase in joy. -Talmud, Taanit 29a

There are many joyous dates on the Jewish calendar, but besides Purim, none of them affect the entire month, causing it to be auspicious and joyous. What is the intrinsic connection between Purim and Adar? Perhaps a comprehension of the unique nature of Purim will allow us to understand why its joy extends throughout the entire month of Adar.

Haman successfully pinpointed the moment when the Jews were at their lowest pointHaman thought to take advantage of the Jews when they were at their lowest point. After nearly a millennium of freedom, independence, and constant reliance on miracles, they were now banished from their land, helpless and seemingly at the mercy of the laws of nature. This was a completely new experience for the Jewish nation. Their spiritual status was also significantly affected. The Temple in Jerusalem where G‑d's presence was manifest, a symbol of the special relationship He shares with His chosen nation, laid in ruins. As for the prospects of its reconstruction — even the gentiles were aware of Jeremiah's prophesy that after seventy years of exile G‑d would return the Jews to their land and rebuild the Temple. Seventy years had elapsed (or so everyone thought, due to erroneous calculations), and the awaited redemption had not arrived.

"The timing has never been better," Haman thought. "Surely the Chosen People have lost their exalted status. Now is the perfect moment to implement the Final Solution."

Haman, however, was not yet satisfied. He needed one more sign indicating the Jews' vulnerability. The lottery would have the final say. And indeed, the lottery provided the exact sign he anxiously awaited. The lottery designated Adar to be the month when his nefarious plan would be put into motion. The Talmud tells us that Haman was overjoyed by this favorable omen. "My lottery fell on the month when Moses died," he exclaimed. The demise of Moses, the "head" of the Jewish nation, was surely a metaphor for the demise of the entire nation!

Haman successfully pinpointed the moment when the Jews were at their lowest point – historically as well as calendar-wise – to implement his plan... But his plan still did not succeed.

Why?

The history of our nation is very much compared to the human lifespan. Through the course of a lifetime every person undergoes drastic changes; fluctuation being the most consistent feature of life. The helpless newborn has virtually nothing in common with the independent, talented personality which will emerge years down the line. Adulthood, too, has ups and downs, happy days and depressing days, fulfilling days and seemingly wasted days. There is, however, one constant: the very identity and essence of the person. John Doe remains John Doe from the day he is born until the day he dies.

our perpetual relationship with G‑d is more evident when we are exiled and downtroddenThe same is true with our nation. We have ups and downs, both spiritually and materially, but our very identity, the fact that we are G‑d's chosen nation, is never affected.

It can actually be argued that, in a certain sense, our perpetual relationship with G‑d is more evident when we are exiled and downtrodden due to our sins, and G‑d still interferes on our behalf, as was demonstrated by the Purim miracle. This phenomenon demonstrates the durability of our relationship; the ability of our essential identity to survive no matter our external state.

All other holidays celebrate the "highs" of our nation. And therefore their joy is limited, because highs don't last. Purim celebrates a time when we were at a low point in our history – but our relationship with G‑d remained intact. Its joy is therefore greater than the joy of any other holiday, because it demonstrates the essential nature of our relationship with G‑d — and that is a constant.

The month of Adar, the month which Haman understood to be the most inauspicious month for the Jews, is the happiest month of the year—the month when we bear in mind that "inauspicious" has absolutely no bearing on our relationship with G‑d.