The Gemara says (and the Shulchan Aruch paskens) “Chayav Inish Livsumei BePuria Ad D’Lo Yada Bein Arur Haman LeBaruch Mordechai” — “a person needs to drink on Purim until he doesn’t know the difference between Arur Haman and Baruch Mordechai.”
Why does the Gemara use such a funny expression? Why doesn’t it just say to drink extra wine to have extra simcha? And isn’t it against the Torah to not know the difference between good and bad?
In halacha there are different explanations for this:
• There was a long song that Yidden used to sing on Purim, that ended with the words “Arur Haman, U’boruch Mordechai,” and you should say enough lechaims that you shouldn’t be able to sing the song until the end.
• You shouldn’t know which is more important — that Haman was destroyed, or that Mordechai was raised up? Which helped the Yidden more — that we got rid of Haman, or that we made Mordechai into the important leader?
• The words “Boruch Mordechai” and “Arur Haman” have the same Gematria, and you should drink enough wine that you can’t calculate the Gematria anymore!
• Some say that it means that you should drink enough that you should get tired and fall asleep, and when you’re asleep you don’t know the difference between Arur Haman and Baruch Mordechai.