Every year, history repeats itself. After the miracle of Purim occurred, the Jews celebrated, making these days into a time of feasting and rejoicing. When we commemorate this today and observe the mitzvot of Purim, the light of these miracles shines on us too, and we receive the divine outpouring of holiness.

The Jewish people create the holiness of Purim:

“These days are remembered and observed” (Esther 9:28); the interpretation of this is that through remembering, and through the reading of the megilla [and the observance of the other mitzvot of Purim each year], the [spiritual] force of the miracle is revived. This is the meaning of the verse: “To make them days of banquet and joy” (Esther 9:22), as through the mitzvot of Purim, these days are made into days of feasting. [Consequently,] during these days, a divine outpouring of holiness and the light of miracles are revealed.

Further reading: For more on the idea that remembering can bring about a renewal of past events, see p. 54.

Joy for the sake of Heaven brings about the light of Purim:

Indeed, that generation put this into effect, as it is written: “And it was made a day of banqueting and joy. Therefore, the Jewish villagers, who live in open towns, make the fourteenth day of the month of Adar [a day of] joy and feasting and a festive day” (Esther 9:18–19). Because they made it into a day of feasting, and their joy was for the sake of Heaven, and they rejoiced at having sanctified His blessed name, [the essence of Purim was established as being joyous] and “[Every] mitzva that they accepted [upon themselves] with joy…they still perform with joy” (Shabbat 130a). Likewise, today, the more we receive these days with joy and for the sake of serving the Creator, the more the days are illuminated [with a heavenly light]. (Rabbi Yehuda Aryeh Leib Alter, Sefat Emet, Purim 5660)

The joy of Purim is the joy of performing a mitzva, and it does not allow for any degree of licentious or unruly behavior:

Even with regard to those individuals who become drunk [at the Purim meal], their intentions should be for the sake of Heaven, in order to remember the miracle, which came about through a wine fest. They should not behave like those people who become drunk in order to fill their throats [to satisfy their desire to get drunk]…and [the notion that] anyone who behaves in a crazed fashion is worthy of praise [is baseless], for all this is certainly wicked and a serious sin. (Rabbi Moshe Met, Mateh Moshe, Inyan Purim 1012)