According to Pirkei D’Rebbe Eliezer (50) Haman intended for Achashverosh to provide the clothing he wore at his coronation. As can be seen in museums around the world, the clothes worn at a coronation or even presidential inauguration are important, and become part of the culture.
The Yosef Lekach explains that these could not just be any clothes, but had to be special and were likely kept in storage for important occasions like this.
R’ Avraham Chadidah writes enigmatically that Haman meant to imply to Achashverosh that his providing the clothes would show that he is a kind, generous man.
R’ Dovid Holtzer explains that the logic behind this depends on how the king defines himself. Achashverosh, from his original invitation of the rich and poor to his party (Esther 1:5), defines himself as a nice, generous person. Similarly, the nuance of clothing defines oneself. The clothing one wears defines one’s political beliefs, religious concerns, cultural status, etc. Therefore, dressing like Achashverosh can make you like Achashverosh in character.
On a more mystical level, R’ David Valle writes that the idea of a king’s clothing refers to the King above rewarding the righteous below. He writes that such rewards come from the forty-five letter Name of H-Shem. Forty-five is also the gematria of the word kacha (“like so”) referring to this reward in the next verse (Esther 6:9) and the gematria of adam (“man”), meaning that H-Shem always rewards the righteous, even when it is not manifestly apparent to us with our limited vision.
The Ibn Ezra writes that this is simply a long time to fast, which demonstrated the Jews’ renewed loyalty to H-Shem.
R’ Yehonason Eibshutz writes that Esther mentions both night and day because days and nights added together equal six regular, Halachic days. This is the amount of time the Jews spent at the seven day feast of Achashverosh (see 1:5) because they were not there for Shabbos.
The Ohel Moshe quotes R’ Yosef Rozofsky that three full days of fasting naturally affect a person’s grace and beauty, which are the characteristics Achashverosh saw in Esther. This is why Esther only fasted for 70 hours, instead of three full days.
The Ben Ish Chai writes that night and day represent different kinds of Torah. The Torah one learns at night should be Oral and the Torah one learns in the day should be from the Written Torah, TaNaCh. Esther’s stressing both of these times means that she wants the Jews to learn both kinds of Torah to gain a closer relationship with H-Shem.
Perhaps she mentions night first because, historically, the Oral Law begins shortly after this period. Megillas Esther is full of hidden miracles, which are flushed out through concentrated, deliberate thought – the very essence of Oral Law.
The Jews responded to this news with a total of six actions: they mourned, fasted, cried, eulogized, and donned sack and ash. The M’nos HaLevi writes that there is significance to this number. These six actions correspond to the six days in which the Jews participated in Achashverosh’s party (see Esther 1:5). Indeed it was a seven-day party, and the Jews took a break from the last day because it was Shabbos.
Since the verse that describes Achashverosh’s party (1:4), the verse says the party lasted for many days (yamim rabim), and gives the number of days as 180, R’ Yehonason Eibshutz wonders why the phrase “yamim rabim” is not superfluous. He answers that this phrase refers to the kind of days they were, long summer days, concluding with Yom Kippur. This is the day on which no Jew sins. In fact, he adds that the gematria of the Satan (hasatan) is 364 (5+300+9+50), one less than the total amount of days in a solar year, indicating that the Evil Inclination has no hold on us for one days out of the year – Yom Kippur. Therefore, there were only six days for which the Jews needed to atone.
The Ginzei HaMelech writes that the Sfas Emes views Megillas Esther as the beginning of the Oral Law. Mordechai was even a member of the Anshei Kenesset HaGedolah (Men of the Great Assembly) that began the establishment of Rabbinic law. The Oral Law is represented by the number six, as that is the total number of Orders in the Mishnah – Seeds, Festivals, Women, Damages, Holy Items, Purity. The Jews mourned in six different ways in to show their new-found reverence for the Oral Law.
Interestingly, according to the Vilna Gaon, there are not six actions here, but five. In his understanding, the great mourning is not a separate action, but is one general action described with the remaining five detailed descriptions. According to him, these five correspond to the five actions Jews are supposed to take (Mishnah, Taanis 1:3-7) when they are suffering agriculturally.