To properly answer this question, let us examine, in what context Purim is taking place. Roughly seventy years have passed after the First Beit Hamikdash was destroyed and the first time in history that the Jewish people as a collective nation found themselves in exile from the time they entered Eretz Yisrael. Indeed this was a very depressing time. Part of their depression was the existential question they were grappling with: Will Hashem’s Shechinah stay with us even in Exile?
The most glaring oversight in the Megillah is no doubt that the name of Hashem is missing. The most common Peirush we are used to hearing is in order to ingrain within us the everlasting lesson that although we don’t always see Hashem in a revealed manner, nevertheless, his omnipresence is within us.
Ribi Yosef BenOualid zt”l son of Ribi Yitzhak BenOualid zt”l in his sefer Samo Yosef explains this phenomenon from a different angle: It is written in the passuk in Parashat Yitro “Anywhere where I will mention my name, I will come to you and bless you” (20:21). He quotes the Sefer Hemdat Yamim who explains why the name of Hashem is omitted in the Megillah, since Hashem does not rest his Presence on Tragedy, and although we were saved, nevertheless “The writing and sealing of the king, cannot be withdrawn”(Esther 8:8 ), and for this reason there was the decree of the Greeks upon us in the Chanuka era. This is why we fast on Taanit Esther. Not only for remembrance of the original decree but to pray every year that the original sin of the generation during the time of Purim should not come to haunt us. This, explains Ribi Yosef BenOualid zt”l is the intention in the passuk “Anywhere where I will mention my name, I will come to you and bless you”, only in places of complete deliverance, not only a temporary Geulah as was in Purim.
However, this still begs a question, what was so great in the Sin of the Generation of Purim to be deserving of such a tragedy? Hachamim teach us that by partaking in the Seudah of Ahashverosh, the decree of Purim fell upon them. On the surface, this is very difficult to understand. Just by partaking in a forbidden Seudah is grounds to destroy the Jewish people?
Achashverosh contented that Hashem’s presence no longer rested with the Jewish people as they were in Exile. As a proof, according to his calculations, the Seventy years have elapsed and the Beit Hamikdash was still left unbuilt as Hashem has promised. Obviously this meant that Hashem has forsaken his people c”v. In order to buttress this point, Achashverosh made a glorious Seudah, in it he exposed the vessels of the Beit Hamikdash. When the Jews partook in this Seudah, the decree of Lehashmid Ulaharog was sealed. This is puzzling? Just because they partook in the Seudah was a reason to destroy his entire beloved nation?
The answer, explain the Mefarshim, is that the partaking of the Jews in the Seudah of Ahashverosh represented a much deeper issue. By partaking in the Kings Seudah, the Jews were actually conceding defeat. They gave in to their grappling existential question and concluded that Ahashverosh must be right. If Hashem did not deliver them yet, it must be his presence is not with them in exile. Depressing indeed.
According to what was explained above, we can properly understand why indeed the sin during the time of Purim was so great. Not merely because they took part in an improper meal, rather the message behind it, that being that Hashem has left us since we are in Galut. For this reason explains Ribi Yosef BenOualid zt”l in the name of the Hemdat Yamim, Hashem’s name is not in the Megillah.