AGADAH: The Gemara says that if a woman walked between two men while she was
a Nidah, then if it is the beginning of her state of Nidah, one of the men
will be killed, and if it is the end of her state of Nidah, a quarrel will
arise between the men.
The VILNA GA'ON (Kol Eliyahu 142) used this Gemara to explain the motivation
behind the seemingly strange conduct of Queen Esther when she arranged to
discuss the situation of the Jews with Achashverosh. Esther invited Haman to
join her and the king at the first dinner she made in the king's honor. The
Gemara in Megilah (15b) questions why Esther invited Haman to come to the
first meal along with the king, when she was not going to reveal herself
until the second meal. The Gemara gives many reasons for Esther's conduct.
The Vilna Ga'on said that "had I been there, I would have added another
reason why she invited him." The Gemara (Megilah 15a) says that when Esther
heard the news of Haman's plot against the Jews, it shocked her so much that
she became a Nidah. Three days later, she made the first dinner party for
Achashverosh and Haman. Her motivation was to invite the two of them and, as
a Nidah, to situate herself between them. If she was at the beginning of her
state of menstrual bleeding, then one of them would die, leading to the
annulment of the decree against the Jews (the Gemara in Ta'anis (29a) says
that when the senate made a Gezeirah, if one person in the senate would die,
then it would be taken as an omen that the Gezeirah must be annulled). If
she was at the end of her state of Nidah, then a quarrel would arise between
Achashverosh and Haman, and again Achashverosh would rescind the decree.
Either way, the decree would be rescinded as a result of Esther's strategy!
(In the end, both outcomes proved true; a quarrel erupted between Haman and
Achasverosh, and Haman was killed.)