Rav Chaim Vital on Ad d’lo Yada

A person is obligated to drink on Purim until he no longer knows the difference between “cursed Haman” and “blessed Mordechai.” (Megilla 7b)

That which our Rabbis, of blessed memory, have said, that a person is obligated to drink on Purim until he no longer knows the difference between “cursed Haman” and “blessed Mordekhai” – this means as follows: It is known that in every kelipa there is a spark of holiness that gives it life, and should it be removed, [the kelipa] will be left with no vitality and immediately it will totally disappear. Now on this great day, when there is this great illumination, we want the vitality of this illumination to reach this spark as well, but not that it should reach so far to illuminate the kelipa. For this reason a person must get drunk on this day, to the point that he does not know the difference between “cursed Haman” and “blessed Mordekhai.” For he may err and give a blessing to that spark in the kelipa, and it too will be blessed, but its blessing will not have perfect intention, for if it would have, it would receive a great deal and the kelipa would also be blessed. [Alternate reading: Therefore he must say “blessed Haman,” to draw light also to that spark, and therefore he must say it without intention, since he is drunk and has already lost his mind. For were it with intention, God forbid, it would also illuminate the kelipa.] (Peri Etz Chayyim, Sha’ar Rosh Chodesh, Chanuka U-Purim, ch. 6)