The Midrash Mishlei states that after Moshiach comes, we will cease to observe all the Yomim Tovim, except Purim. Many commentators have asked why this should be. Was Purim as momentous as the Exodus from Egypt, or the giving of the Torah at Sinai? Furthermore, Purim is a rabbinically instituted, so why should it be celebrated when Yomim Tovim in the Torah are not?
The Sfas Emes asks another question. The Megilla clearly states that Purim is עַל-שֵׁם הַפּוּר – because of the lottery performed by Haman.
Why do we refer to it in the plural form – Purim – to refer to this Yom Tov which celebrates a single lottery? Secondly, the lottery was hardly the primary part of the miracle of Purim. Why would we name the Yom Tov after an un-miraculous and perhaps even incidental event?
The Sfas Emes explains that we would only use the name Purim if the “pur” was an integral part of the nes. When Haman cast his lots, it was “לְהַשְׁמִיד לַהֲרֹג וּלְאַבֵּד” – to utterly destroy the Jews. Yet, as the eternal nation, the Jews cannot ever be completely destroyed, meaning that Haman’s plot was doomed to fail from the very beginning. The “pur” therefore was dual in nature. On the surface it appeared to be detrimental for the Jews, yet by it’s very design condemned Haman to fail and thus lead to the Jews’ salvation. To reflect this duality, we refer to Purim in the plural to underline that even events that seem ‘bad’ are a part of Hashem’s plan and turn out for the good of Klal Yisroel.
The Vilna Gaon in his commentary on Esther explains that this is why we will celebrate Purim after Moshiach. Previous miracles where Hashem has revealed Himself and performed supernatural miracles will be eclipsed by the miraculous events surrounding the coming of Moshiach. The Yomim Tovim commemorating these events will no longer be celebrated because the events they recall will be of secondary importance in comparison to those we will witness in the future. Purim however, occupies a unique space amongst the other Yomim Tovim. It recalls that Hashem’s hand guides our lives and that all events are controlled by Him even if we do not openly see Him. Thus we will continue to celebrate this unique Yom Tov that offers us a glimpse of His master plan that guides nature even when Yomim Tovim celebrating supernatural events are no longer celebrated.