A kohen gadol can't marry a widow (see Vayikra 21:14). What is the reason for this prohibition?
The Chida (Pnei David, Emor) explains that when the kohen gadol came to the Kodesh Hakadoshim on Yom Kippur to do the avodah, he would say the המפורש שם – Hashem’s name ה"הוי, as it is written. When the kohen gadol uttered this name, if he thought that someone should die, it would happen.
If he would be permitted to marry a widow, he may choose to kill a husband when he uttered Hashem's name on Yom Kippur so he could marry his wife. To prevent this, the Torah says a kohen gadol may not marry a widow.
Doesn’t it seem far-fetched that such a murder would ever happen? On Yom Kippur, the holiest day of the year, the kohen gadol, one of the nation’s greatest people, in the Beis Hamikdash, in the Kodesh Kadoshim, saying Hashem's holy name – something only he can say, and only on Yom Kippur – could it be that at this sacred moment, he might intend to kill someone to marry that person’s wife? Apparently, it could happen.
Indeed, Chazal (Succah 52.) say, מחבירו הגדול כל הימנו גדול יצרו, “The greater a person, the greater his yetzer hara,” and Reb Yechezkel Levinstein zt’l adds, “The greater the moment and time, the greater the yetzer hara.” Therefore, it could happen. The Torah understands the yetzer hara and knows that even this is possible.
We mention this so we shouldn't be surprised that the holy mitzvah of drinking on Purim could result in something negative. Unfortunately, some people don’t understand this. They say, "Purim is one of the holiest days of the year, and drinking is a mitzvah. So, how could anything negative come from it?
But don't be surprised. Drinking excessively could be damaging and could lead to sin; therefore, fortunate are those who are cautious to drink with wisdom and know their limits.
