It states (Esther 5:6), היין במשתה לאסתר המלך ויאמר ותעש המלכות חצי עד בקשתך ומה לך וינתן שאלתך מה, “The king said to Esther at the wine party, ‘What is your request, and it will be yours... Ask for half the kingdom, and it will be granted to you.” The Minchas Elazar zt’l says this pasuk means that on Purim, when we are at the היין משתה, wine party, the King of the world says to the Jewish nation, מה לך וינתן שאלתך, “What is your request? Ask for whatever you want, and I will grant it to you.”
Chazal say, בפוריא לבסומי איניש חייב, a person is obligated to be happy with drinking on Purim. לבסומי isn't a very common word. It is written only a few times in Shas. Interestingly, the Gemara uses the word לבסומי twice on the same page (Megillah 7:), and it is used with two different translations. The Gemara says that on Purim there is a mitzvah לבסומי, to drink wine. A few lines above that, the Gemara uses לבסומי to mean sweet. The Gemara says, שכיחי לבסומי רווחא, "A person always has room to eat something sweet."
The Gemara relates that one Purim, Abaya came to Mari bar Mar's home to deliver mishloach manos. Abaya said that he didn’t feel hungry when he came to Mari Bar Mar’s house. Mari bar Mar served him sixty plates with sixty types of cooked dishes, and Abaya ate them all. The final course was pot roast, and Abaya said he had a great appetite; he even wanted to eat the dish. The Gemara says, ידע ולא עניא כפין אינשי דאמרי היינו, “This is as people say, ‘The poor are hungry, and they don’t know it.’ שכיחי לבסומי רווחא ,נמי אי, Or it is as people say, ‘One can always find room for sweets.’”
לבסומי has two translations. It means sweets, and it means being happy through wine. The Yetev Lev zt’l connects the two Gemaros and explains that if one is בסומי בפוריא, happy with wine on Purim, לבסומי רווחא שכיחי, he will have והצלה רווח salvations and בסומי sweetness in his life.
The Imrei Emes said that בסומי is roshei teivos for (Tehillim 119:120), וממשפטיך בשרי מפחדך סמר יראתי, “My flesh bristles from fear. I am afraid of Your judgment.” This hints that one should drink wine with yiras Shamayim. Additionally, this implies that one can attain yiras Shamayim from this mitzvah.
The Mishnah states (Beitzah 40.), ושוחטין משקין, we give the animals water to drink before we slaughter them. This is because it is easier to skin an animal after it drinks. We can explain that skinning an animal is akin to a human being shedding his animalistic nature and attitudes. Thus, we can explain משקין, by drinking on Purim, one sheds his animalistic self and becomes a more spiritual being.
The Sfas Emes (Purim 7635) writes, "Purim is like Yom Kippur. Yom Kippur, we go beyond nature with fasting, and on Purim, we rise above nature with eating and drinking."
Once, a chassid was planning to take his daughter to a doctor on Purim. Rebbe Avraham Elimelech of Karlin-Stolin zt’l hy’d told him, “Purim, we attain refuos from drinking, not from doctors.” The Rebbe gave the father some wine and told him to give it to his daughter. The girl drank the wine and was cured.
