The Talmud (Megillah 7a) learns from the verse’s use of “feasting and joy” that there is a mitzva to drink ad d’lo yada, until one does not know the difference between “cursed is Haman” and “blessed is Mordechai” on Purim. Although this a topic worthy of a much larger Halachic discussion, it should suffice for purposes of understanding this verse to note some varying opinions on this subject.
Indeed several Halachic deciders understand this literally as an injunction to become completely drunk on Purim, as is clear from the Rif (Megillah 3b) and the Tur (OrachChaim 695:2).
Among others, the Peleh Yo’eitz warns that, obviously, this drinking should not be done to the point where one would miss any other mitzvos, including praying mincha with proper intent.
The Talmud (Pesachim 68b) teaches that holidays from the Torah should be be split evenly – half for H-Shem (i.e. with prayer, learning, etc.), and half for our own pleasure (i.e. eating, resting, etc.). However, even according to an earlier opinion there that all holidays should be completely for H-Shem, this verse’s use of the words “feasting and joy” require Purim to be completely for our pleasure.
The Abudraham notes that drinking is such a critical part of celebrating Purim because drinking plays a central role in Megillas Esther, including Vashti’s fall (Esther 1:10), Esther’s rise (Esther 2:18), [the decree to kill the Jews (Esther 3:15),] and Esther’s parties that led to Haman’s fall (Esther 7:1-10).
The Midrash Eliyahu writes that we celebrate Purim by drinking because the Talmud (Megillah 13b) relates that Haman slandered the Jews’ drinking practices when he told the king that if a fly were to touch a Jew’s cup, he would remove it and continue drinking. However, if the king were to touch a Jew’s cup, the Jew would throw the wine away, alluding to the Talmudic (Avodah Zarah 30a) law of yayin nesech.
The Nesivos Shalom (Purim 57-58) has a very unique reading of this Talmudic passage. He notes that the above cited teaching does not say “livsumei” (“to become intoxicated”) with wine, but rather “livsumei” in Purim. This means that one should get drunk from the day of Purim, itself, similar to the prophet’s (Yeshaya 51:21) description of being “drunk, but not from wine.” Through prayer, Torah study, and acts of kindness, Purim should cause a person to become so “drunk” on the elevated revelations of Purim that one cannot tell the difference between “cursed is Haman” and “blessed is Mordechai.”
Malbim writes that the joy mentioned in the verse parallels “feasting and joy,” while the holiday parallels the sending of gifts. This is so because the very purpose of our lives is to separate ourselves from the physical in an effort to focus on the spiritual. That is the very-same purpose of Yom Tov!
Similarly, in Horeb, Rav Hirsch writes that the physical rescue of the day deserved a physical enjoyment.
Similarly, in R’ Tzaddok HaKohen’s contrasting between Purim and Chanukah, he focuses on the fact that Chanukah was a struggle between different philosophies, wherein the Hellenists and Greeks did not care if the Jews lived or died as long as they accepted the Hellenistic worldview. Therefore, Jews celebrate Chanukah, which was a spiritual/philosophical victory, in a spiritual manner, with additions to the daily tefillah and the lighting of the chanukiya. Jews celebrate Purim, on the other hand, which was a physical victory, in a physical manner, with feasting and joy.
The Bach (Orach Chaim 670) focuses his distinguishing of the two days by noting that the entire Purim story was initiated by the Jews wrongly attending Achashverosh’s feast. He quotes a Braisa that says that the Chanukah story was perpetuated by the Jews’ lack of alacrity and laziness in fulfilling the tamid offering. Therefore, Purim is celebrating with a party to make up for our attending Achashverosh’s party, and Chanukah is celebrated with the lighting of Chanukah lights to make up for the neglecting of the constant fire of the tamid offering.
His son-in-law, the Taz (Orach Chaim 670:3), writes that Purim is an open miracle that saved our temporal lives, wheras Chanukah commemorates a relatively hidden, spiritual miracle in the oil lasting longer than expected. Their distinct commemorations, then, are accomplished through the public feasting of Purim and through the relatively private lighting of the Chanukah menorah, respectively.
The Sfas Emes adds that our physical pleasure on Purim is also due to the physical nature of Eisav’s (progenitor of Amalek) blessing that Yaakov (progenitor of the Jews) took from him (Bireishis 27:28-29). Furthermore, Yaakov’s attempt to take on Eisav’s physical role in the world is yet another reason for the custom to wear masks on Purim.
During a Purim seudah, the Satmar Rebbe once mentioned that one might have thought that Haman’s idol would make the threat to Jewish existence on Purim a spiritual one. However, the physical and spiritual aspects of a Jew are one and the same. After all, a physical body without a soul is a corpse. Accordingly, this is another reason for the custom to drink on Purim – to see beyond the superficial, and realize that our physical health is directly related to our spiritual health.
The Ben Ish Chai writes that the mitzvos of the day are intended to make Purim a day of Heavenly purpose of spiritual growth, and not for selfish joy. He bears this out from the fact that the initial letters of the four mitzvos of the day – simcha, mishteh, yom tov, manos – can be seen as an acronym that spells out shamayim (Heaven).
Famously, the Ari z”l quotes the Tikkunei Zohar (21) that the holiness of Yom Kippur is due to its being a “yom kiPurim” (“a day like Purim”).
The Ohel Moshe suggests that Yom Kippur’s holiness depends on Purim because the Talmud (Taanis 30b) says Yom Kippur was the day on which Moshe came down Mt. Sinai with the second set of luchos (“tablets”). This receiving of the Torah was not complete until the Jews accepted the following of its commands in the days of Purim with the verse’s (Esther 9:27) words “kimu v’kiblu.”
On another level, R’ Yitzchak Hutner explains that Purim is similar to Yom Kippur because there is a need on both days to make things right with people. The Mishna (Yuma 8:9) teaches that a person does not gain atonement for the wrongs one caused to another unless one asks for forgiveness from that person. Similarly, on Purim, the sending of mishloach manos is supposed to engender feelings of unity and peace among the Jewish people. This is done in a spiritual manner – by begging for forgiveness – on Yom Kippur, and in a physical manner – by drinking and feasting together – on Purim. In this way, the two holidays compliment each other, and become one powerful entity.
On one particular Purim in the Warsaw ghetto, R’ Kolonimus Kalmish (Hy”d) approached a Jew who was understandably not feeling joyous in the midst of terrible atrocity. He told this Jew that the intent of the comparison between Purim and Yom K’Purim is that just like a Jew should feel like there is no choice on Yom Kippur, and one must fast, so too, on Purim, one has no choice – one must have simcha (“joy”)!