We read in the Gemara that on Purim one must drink “until he cannot differentiate (“ad d’lo yada”) between ‘cursed be Haman’ and ‘blessed be Mordechai.’ ”
The Rebbe explains: The goal of ad d’lo yada (literally, “until he does not know...”) is that a person reach a level of utter subservience to HaShem, which is not limited by his own understanding, and through this, all undesirable perspectives will be washed away. As a result, one will have the strength to continue this avoda throughout the entire year.
(מגילה ז,ב, לקו"ש ח"ד ע' 1277)
On the first Purim after his chasuna, the Alter Rebbe gave a non-literal exposition of the avoda of attaining the level of ad d’lo yada. On Purim, he said, we must ensure that the lo – literally, “the No,” that is, the things that are forbidden – should be yada (“known”). What we are supposed to do is well known, but one must also know what is forbidden, so that it can be treated with extra caution.
(סה"ש תש"ה ע' 72)
The Megillah says that after the miracle of Purim, the Yidden were blessed with simcha (“joy”), which Chazal understand to mean that they were now able to celebrate the Yomim-Tovim. The Rebbe explains that although other nations also have holidays, they celebrate them with drinking and unbridled conduct. Yidden, by contrast, even when they rejoice and drink they become closer to HaShem, and heighten their yiras Shamayim and holiness.
(לקו"ש ח"ג ע' 920, ח"ד ע' 1274, וראה שוע"ר סי' רצ"ב ס"ג)
CONSIDER
How can the merrymaking on Purim be both a source of brachos and a distraction from it?
If Purim is really a Yom-Tov why is it permissible to do melacha?
