Unfettered By Intellect
A Mitzvah to Drink
The Talmud  states that "on Purim we are obligated to drink wine to the point where we do not know the difference between 'Blessed be Mordechai!' and 'Cursed be Haman!'."
Our Rabbis  point out that according to the rules of gematria, the letters that constitute the two phrases have the same numerical value; our Sages' injunction means that we should drink to the point that we are unable to realize this relationship.
But once a person is intoxicated, he is incapable of even the simplest numerical computation; why, then, do the Sages tie the amount of wine one is obligated to drink on Purim to this particular gematria?
This question can be answered by realizing that a numerical correspondence between two words in gematria is not coincidental, but reveals an intrinsic bond between them. 
The Torah  states that G-d created the world through speech.
The Alter Rebbe explains  that the letters that spell out the Hebrew name of an object comprise the conduit which conveys its G-dly life-force, bringing it into being and maintaining its existence.
It follows that if there is a letter-relationship between the names of two objects, there is also an underlying spiritual relationship between them. Hence, though the expressions "Blessed be Mordechai" and "Cursed be Haman" appear to be diametrically opposed, their shared numerical value reveals a basic similarity between them. The same Divine intention motivates both of these expressions.
Deriving Positive Input from Haman
Nothing created by G-d has a negative purpose.
In some cases, G-d's positive intention is openly manifest; in others, He desired that man reveal His positive intention by transforming apparent evil into good.
G-d created Haman (as well as everything else that appears to be evil) so that the Jewish people could bring about a fundamental change in the nature of evil and transform that which is evil into good.
It is for precisely this reason that the Sages obligate us to blur the distinction between "Blessed be Mordechai" and "Cursed be Haman."
On Purim we are required to elevate our understanding to the point that we perceive no essential distinction between Mordechai and Haman. For the ultimate goal in the creation of Haman is that he become a force for good, like Mordechai.
The events of Purim exemplify this concept.
The threat posed by Haman endangered the very existence of the Jewish people. In response, they demonstrated self-sacrifice and dedication to Torah which transcended the limits of reason. Their commitment transformed the entire nature of the situation. Thus, instead of destroying our people, Haman's plot enriched us with a festival and a day of rejoicing.
A Constructive State of Not-Knowing
Given that we can intellectually understand the true relationship between "Blessed be Mordechai" and "Cursed be Haman" without drinking, why is it necessary to drink on Purim to the point of intoxication?
Why is the intellectual exercise not enough?
To answer this question, we must consider the concept of "not knowing."
Generally, we consider "not knowing" to be a negative state, a deficiency in sensitivity and awareness, while "knowing" is seen as a sign of personal development.
There are, however, two states of "not knowing," one that is inferior to conscious knowledge, and one that transcends it.
Within the limitations of this world, understanding represents the highest of our faculties.
G-d's essence, however, is not bound by the limits of our faculties: it transcends all definition and restriction.
Moreover, G-d's infinite capacity is reflected in our souls; each of us possesses "a spark of G-d"  that is unrestricted. From this perspective, we can understand the adage, "The ultimate in knowledge is not to know." 
Reason is, by nature, limited and prevents the expression of our unlimited potential, which can be tapped, not through "knowing", but by rising above our powers of understanding. This mode of divine service - self-transcendence - is the goal of our drinking on Purim.
For Darkness to Illuminate
The state which transcends the limits of reason is related to the concept of transforming evil to good.
From an intellectual perspective, good and evil have clearly defined boundaries: mitzvos help us connect with G-d and sin draws us away, obstructing our relationship with Him. 
However, the infinity of G-d's essence (and likewise, the infinite potential of our souls) is not bounded by these limitations. At this level, "darkness is like light."  Even sin and evil cannot prevent us from returning to G-d.
Regardless of a person's current state, he always remains able to reorient his life, to turn to G-d in teshuvah, and to leap over all the obstacles created by sin.
Not only that, but our Sages explain  that through teshuvah motivated by love, even "purposeful sins become merits." Through connecting with G-d at this level, the G-dly life-force that was overlaid by sin is transformed into good.
In light of this, we can understand our Sages' teaching  that "In a place where baalei teshuvah stand, even perfect tzaddikim cannot stand." The divine service of a tzaddik engages those more reachable aspects of G-d's will that have been garbed within the limits of the Torah and its mitzvos.
The spiritual momentum of a baal teshuvah, however, catapults him to a level of Divine connection that defies all limitation.
An Unlimited Commitment
This concept of unlimited commitment is intrinsically related to Purim; it is even alluded to in the name of the holiday. 
Purim means "lots", and casting lots symbolizes a step above the realm of the rational. (For this reason, lots were used to determine which of the two prepared goats was to be sent to Azazel in the Yom Kippur service in the Beis HaMikdash. )
In this spirit, during the time of the Purim miracle, the Jews rose to a level of commitment that transcended the realm of intellect. They were prepared to sacrifice their very lives for the sake of the Torah.
Their inspired commitment and its expression in actual deeds brought about the transformation of evil into good: a great miracle occurred. Instead of the annihilation of the Jewish people, we merited great deliverance. Moreover, Haman's house  and position were handed over to Mordechai and "many from among the people of the land became Jews." 
The AriZal,  commenting on the verse,  "And these days are recalled and celebrated," teaches that when a holiday is "recalled" properly, when it is relived, the same spiritual influences which were originally revealed become "celebrated" and actualized every year anew.
Thus, our current efforts to transcend our selves and rise above our intellectual limitations will surely bring about a process of transformation in the world. The darkness of exile will give way to the light of Redemption.
Adapted from Likkutei Sichos: Vol. VI, Purim; Vol. VII, Parshas Vayikra
- (Back to text) Megillah 7b.
- (Back to text) Agudah, quoted in Darchei Moshe, Orach Chayim 695, Bayis Chadash (loc. cit.).
- (Back to text) Cf. Shomer Emunim, First Dialogue, sec 21-23.
- (Back to text) Bereishis, ch. 1.
- (Back to text) Tanya, Shaar HaYichud VehaEmunah, ch. 1.
- (Back to text) Tanya, ch. 2.
- (Back to text) Ikkarim 42:30; Shelah 191b.
- (Back to text) See the interpretation of Yeshayahu 59:2 in Tanya, Iggeres HaTeshuvah, ch. 5.
- (Back to text) Tehillim 139:12.
- (Back to text) Yoma 86b.
- (Back to text) Berachos 34b; Rambam, Hilchos Teshuvah 7:4.
- (Back to text) See Torah Or, p. 99d ff.
- (Back to text) The parallel between the two holidays is further reflected in the Biblical name - Yom Kippurim, which Tikkunei Zohar (sec. 21) understands on a non-literal level of interpretation to mean "a day like Purim" (as if it were vocalized Yom kePurim).
- (Back to text) Esther 8:2.
- (Back to text) Ibid. 8:17.
- (Back to text) Ramaz, cited in Sefer Tikkun Shovavim; Lev David by the Chida, ch. 29.
- (Back to text) Esther 9:28.