Purim marks a transition point in Jewish history. It ushers in the time period of hester panim, the transition from G-d's obvious and active role in history to a period when G-d's role in history is difficult to discern. Esther, whose very name is an allusion to this concept of hiding, is the last of the prophets. No longer would the word of G-d be directly revealed to man. There would be difficult choices to make, and man would have to work hard to try to determine the best course of action devoid of direct Divine guidance.
While the loss of prophecy is traditionally viewed in a negative light, bespeaking the downgrading of the special relationship between G-d and the Jewish people, it need not necessarily be seen as such. During the early years of the Jewish nation, we needed overt miracles and many prophets to impress upon us the primary role of the Almighty in all that unfolds in history. A nation formed in slavery could not appreciate G-d through philosophical speculation or intellectual acumen; they had to see the hand of G-d in action. Difficult decisions were made for them; the role of the Jewish people was to follow the word of the prophets. This was something we often failed to do, but our course of action was laid out for us.
Yet there came a time when the Jewish people had to make their own difficult choices. Without direct communication from G-d, we could no longer just ask the prophets what G-d wanted us to do; we ourselves were left to make that determination. And that independence was a most positive development. The time had come for us to leave our parents' home, so to speak, and establish our own. It was hard at first, but it was the only way we could develop our potential as a nation. Our tradition teaches, chacham adif menavi, a sage is better than a prophet (Bava Batra 123a). We would have to work harder to create a bond with G-d, but that bond would be much stronger.
Purim marks the last of the Biblical holidays, the Bible being the word of G-d (or, as far as the Nach is concerned, Divine inspiration), and the beginning of the Rabbinic period. Torah would no longer be in heaven. It was on Purim, our Sages teach, that the Oral Law, forced upon us at Sinai, was finally willingly accepted. The written Torah is the direct word of G-d, unchanging and unchangeable; the Oral Law, though originating at Sinai, must be developed by man in each generation. With the Almighty's role hidden, it becomes difficult to see His miraculous hand working behind the scenes.
The last chapter of the Megillah describes the taxes that Achashverosh imposed on the people. Life went on as usual, and for those living in Shushan over the nine-year period in which the megillah takes place, nothing obviously warranting a holiday had occurred. The miracle went unnoticed. In fact, the Talmud teaches that Hallel, the hymns of praise in recognition of G-d's miracles, is not recited on Purim as acati avdei Achashverosh, we remained subservient to Achashverosh (Megillah 14a). Unlike the Exodus from Egypt, nothing really changed. It is no wonder the Sages initially refused to establish Purim as a holiday (Megillah 7a). Only the persistent efforts of Esther, who (true to her name) could see G-d in His hiding place, enabled Purim to become the beloved holiday that we know.
We live in the shadow of Purim, where one must look hard to see the miracles of G-d on behalf of His special nation. With so many of Haman's descendants plotting to "destroy, to kill, and to uproot all of the Jews from young to old, children and women" (Esther 4:13) we, not unlike the people of Shushan, often fail to see the mighty hand of G-d. Yet despite the hardships, there is much to be grateful for. Just because nothing seems to change does not mean great miracles are not happening right before our eyes. May the Jewish people be blessed with "light and happiness and joy and beauty" as we rejoice in the miracles "in those days, in our times".