(5) At the end of this period, the king gave a banquet for seven days in the court of the king’s palace garden for all the people who lived in the fortress Shushan, high and low alike. (6) [There were hangings of] white cotton and blue wool, caught up by cords of fine linen and purple wool to silver rods and alabaster columns; and there were couches of gold and silver on a pavement of marble, alabaster, mother-of-pearl, and mosaics. (7) Royal wine was served in abundance, as befits a king, in golden beakers, beakers of varied design. (8) And the rule for the drinking was, “No restrictions!” For the king had given orders to every palace steward to comply with each man’s wishes.
שאלו תלמידיו את רשב"י מפני מה נתחייבו שונאיהן של ישראל שבאותו הדור כליה אמר להם אמרו אתם אמרו לו מפני שנהנו מסעודתו של אותו רשע
The students of Rabbi Shimon bar Yoḥai asked him: For what reason were the enemies of Jewish people, a euphemism for the Jewish people themselves when exhibiting behavior that is not in their best interests, in that generation deserving of annihilation? He, Rabbi Shimon, said to them: Say the answer to your question yourselves. They said to him: It is because they partook of the feast of that wicked one, Ahasuerus, and they partook there of forbidden foods.
(טו) כֵּיצַד חוֹבַת סְעֵדָּה זוֹ. שֶׁיֹּאכַל בָּשָׂר וִיתַקֵּן סְעֵדָּה נָאָה כְּפִי אֲשֶׁר תִּמְצָא יָדוֹ. וְשׁוֹתֶה יַיִן עַד שֶׁיִּשְׁתַּכֵּר וְיֵרָדֵם בְּשִׁכְרוּתוֹ.
(15) 15 How is the obligation of this meal? That one eat meat and prepare as pleasing a meal as his hand can [afford]. And he should drink wine until he becomes intoxicated and falls asleep from his intoxication.
(ב) חייב אינש לבסומי בפוריא עד דלא ידע בין ארור המן לברוך מרדכי: הגה וי"א דא"צ להשתכר כל כך אלא שישתה יותר מלימודו (כל בו) ויישן ומתוך שישן אינו יודע בין ארור המן לברוך מרדכי (מהרי"ל) ואחד המרבה ואחד הממעיט ובלבד שיכוין לבו לשמים
(2) 2. One is obligated to be intoxicated on Purim to the point where he does not know [the difference] between "accursed is Haman" and "blessed is Mordechai". RAMA: Some say it is not necessary to become drunk so much, but rather to drink more than he is used to (Kol Bo), and to fall asleep, and while he sleeps he does not know [the difference] between "accursed is Haman" and "blessed is Mordechai" (Maharil). [There is no difference on Purim] between one who has more and one who has less, as long as his heart is directed to heaven
We drink on Purim to commemorate the amazing miracle that occurred. We drink wine because all of the miracles that happened on Purim happened through wine: Vashti was deposed through a banquet of wine and Haman’s downfall was likely started by wine (the feast he was at with Esther and Achashverosh). Everyone should drink to his or her own extent and one should not drink until he or she throws up. When we say that we must not be able to tell the difference between Haman and Mordechai, this also includes when we are asleep, so one can drink a little and then go to sleep and he/she will still be fulfilling the Mitzvah. One who has a lighter tolerance should not drink too much; you just need to drink more than you usually do. When we drink, we should be thinking about how we are doing this to commemorate the huge miracles that happened and the fact that we are alive, we should be thankful to Hashem and all that He has given us.