CHAYAV INISH LEVESUMEH B'PURYA
A person must get inebriated on Purim
There are two types of love:
a) there is the love a man has for his friend, which is conditional and goes according to ta'am v'da'as (reason). Because he understands in his mind (da'as) the benefit to himself, he has love for this thing. This ahava is inherently limited according to his degree of appreciation, more or less appreciation (da'as) leads to more or less love.
b) The love of a son to his father, even if his father hits him and gives him rebuke his love remains firm because it is not dependent on his mind (da'as) because he himself doesn't know the reason he loves his father--it is without ta'am v'da'as (reason).
Both kinds of love exist between Israel and the Holy One, blessed be He. The first is not for everyone except one who has a deeply developed knowledge of G-dliness. However the second kind of love is in all Israel, even the rebellious and willful sinners, because, they are called "sons" and they are a chelek Eloka mi'ma'al ("truly a piece of G-dliness from Above"). This love is very concealed in them, in a state of exile, and only through being trodden down by suffering does it get released from concealment.
The avodah (Divine service) which comes from the core ahava doesn't change ever since it's source is the "piece of G-dliness from Above", as it states "I am YKVK, I didn't change", and is called the Tree of Life which lives forever, without change, because he doesn't take his own being into account to see whether it seems to him good or bad, rather all that he sees is that everything is Hashem's G-dly life force, and there is nothing else besides Him, seeing nothing but Hashem. His very existence is nullified before the will of Hashem, which is the level of Mordechai, refined without any impurities, not seeing himself as separate at all from Him and not wanting anything for himself at all since he is considered as nothing before the Ein Sof, baruch Hu (the Endless, blessed is He).
Haman was the total opposite of this, all of his deeds were only to benefit himself like the nations of the world that "all the good they do is for their own aggrandizement." So the gemara asks Where is Haman in the Torah what is his source? The answer: hamin ha'etz, from the tree, meaning the Tree of Knowledge. Haman is the level of Amalek, of whom it is said "when you will be given relief from your enemies...wipe out the memory of Amalek."
First a person needs to know how to love Hashem, and if he wants then to wipe out Amalek, which is the level of "for his own benefit" (i.e., to serve Hashem without any benefit to himself), he won't succeed and the result will be that he won't do any avodah at all. First, he needs to go out of Mitzrayim (Egypt), which refers to the limitations of gashmiyus (physicality), even the limitation of "for his own sake", and afterwards he will wipe out the memory of Amalek.
Amalek attacked Israel when they came out of Mitzrayim, meaning in the middle of the way as they go from limited to unlimited in mind (da'as). This pains Amalek, the level of "for his own sake". Also, the meraglim (spies) mention Amalek, as they wanted to go up to Eretz Yisrael, which is above spacial limitations. This is where Amalek sits and conceals himself.
One who reaches such a level where he perceives G-dliness in everything can transform his heart and can wipe out Amalek, but this requires a tremendous battle. It is preferable to reveal the hidden love within, that he will nullify his will before His will, and so This is why a person is obligated to drink on Purim, meaning "to make others drink" until "ad d'lo yada" ("he doesn't know"), meaning there is no level of da'as, until he doesn't know the difference between "cursed in Haman" and "blessed is Mordechai", which (between them) is the level of Amalek. One who is extraordinarily holy and wise can come to a "complete heart" ("lev shalem") via his da'as, and then to a "desirous soul" ("nefesh chafeitza") as well. This is not the case for one who is not complete, has not perfected his mind (da'as) -- it is impossible to overcome Amalek (i.e., self-interest) other than through joy, which is above da'as... himself as the Good Inclination, basing himself on the rationale of Torah. enters, secrets come out" because wine can reveal the hidden things, just as the wine itself was concealed in the grapes and pressed out from them, so too one who drinks the wine will reveal what is inside him (i.e., this hidden love of Hashem). This is "wine makes joyful the heart of man", since the concealed is brought out to revelation his joy is awakened, because joy is also a revelation of his inner being (pnimiyuso), and thus the entire tochacha (rebuke) is "because you didn't serve Hashem your G-d with joy".