“… and these days of Purim shall not be revoked from amidst the Jews” (Esther 9:28).
The events of Purim were so momentous that the Sages state that Israel accepted the Torah anew at the time of Achashverosh. In a certain sense, their renewed commitment at that time was greater than their original acceptance of the Torah on Mount Sinai, as emphasized in Talmud:
“They fulfilled [the Torah] – that which they had previously accepted”. (Shabbat 88a).
The Chassidic teaching explains that even when the exile (Galut) comes to an end, the holiness and the virtue of the holiday will continue to shine by their own power and we shall celebrate it forever.