According to the Malbim, by saying the next party will be “according to the word of the king,” Esther was implying that her only motivation in making a request of the king is that the king, himself, asked her to do so in the previous verses.
R’ Elisha Galico says Esther was stroking the king’s ego by implying that only Achashverosh could give Esther what she wanted.
Rashi writes that Esther was suggesting that she was going to finally acquiesce in revealing the secret of her ancestry, which Achashverosh has been asking her for years (see Esther 2:10).
The Vilna Gaon says that Mordechai knew that Esther, being a righteous woman, never voluntarily submitted to Achashverosh carnally. In addition to the fact that he was a gentile, we learned earlier that Esther was married to Mordechai before she was forcibly removed from his home. Accordingly, Esther would need the force of a command to submit to Achashverosh voluntarily. There is a story told of a community rav who was in a situation in which circumstances were such that he had to build a synagogue where a mikvah once stood. Otherwise, his congregation would have no home. Knowing that Halacha (see Igros Moshe, Choshen Mishpat I, Siman 40) does not allow for a shul to be built in such a place, he asked the Chazon Ish for advice. The Chazon Ish reportedly told the rav that he was right, and that building the shul in such a location would earn him punishment in this world and the next. Nevertheless, he still had to do it. His congregation needed a home, and, as a leader, he had the responsibility to accept punishment for their benefit. Here, too, Esther was required to perform this sin for the benefit of the entire nation. Esther would not have gone to Achashverosh voluntarily.
R’ Moshe Dovid Valle quotes the verse in Koheles (3:7) that there is “a time to be silent, and a time to speak.” In other words, Mordechai was telling Esther that there was a time when he commanded her to remain silent regarding her ancestry (see 2:10); now, he was rescinding that command and telling her to speak.
R’ Dovid Feinstein gives another reason why Esther needed to be commanded. Quoting a Rashi in Vayikra 6:2 (in Parshas Tzav), he writes that the word, “tzav” (“command”) is only used when the person performing the action is reluctant to do it because there is something they stand to lose. Here, Mordechai has to command Esther because he realizes her self-sacrifice. Recalling that Mordechai is speaking to Hasach (Daniel) that he has to command Esther because he is a greater Torah scholar. As such, Esther would be more likely to listen to the command.
One might think that the reason for Mordechai’s refusal to bow is the low regard with which the Torah holds worship of anyone or anything outside of H-Shem. According to the Midrash (Esther Rabbah 7:8), however, Mordechai admits that bowing down to a person in-and-of-itself is not wrong. For example, Yaakov and his family bowed seven times to Haman’s ancestor, Eisav (Bireishis 33:3). In fact, Mordechai deflects criticism of his not acting likewise with Eisav’s descendant by citing his ancestry from Benyamin, who had not yet been born during this incident. The Maharal adds that, in reward for this, Benyamin inherited the part of Eretz Yisroel where the Kodesh Kedoshim (Holy of Holies) of the Beis HaMikdash would stand. Mordechai was concerned that bowing to Haman would cause him to lose his connection with the Shechinah (the Divine Presence), just as the Shechinah left the Kodesh Kedoshim when the Jews no longer deserved her.
In Michtav M’Eliyahu, R’ Eliyahu Dessler writes that Mordechai’s defiance can teach us to attack our Yetzer Hara head-on without a kernel of compromise. Any capitulation can lead to a downward spiral of spiritual loss.
The Malbim writes that Mordechai did not bow down to Haman to avoid ascribing divinity to him. In an era when people ascribed godliness to their rulers and the rulers’ courts, Mordechai felt compelled to demonstrate his variance with heaping any possible blandishments of divinity upon Haman.
Rav Eliezer Ashkenazi writes that the command to bow to Haman referred to two different groups of people – regular subjects of the king, and higher-ups sitting at the gates of the king. Mordechai did not fit into either category. As a Jew, he was not a citizen of the realm. At the same time, as an adviser of the king, he sat at the king’s gate, and was not one to pass there.
The Kedushas HaLevi says there were two different commands – first, everybody had to bow down. Second, Mordechai, as a favor to Esther, was ordered to not bow.
The Shelah HaKodesh quotes an argument in the Talmud (Megillah 12a) regarding the reason the Jews deserved death in this time period. One opinion is because they bowed to idols. The other reason is that they attended Achashverosh’s party. The Shelah continues that Mordechai’s refusal to bow to Haman served as a spiritual tikkun (or repair) for the Jews’ capitulating to bow to the idol of Nebuchadnetzer, and Esther’s eating seeds to avoid eating non-kosher food in Achashverosh’s palace (as mentioned previously) served as a tikkun for the Jews’ enjoying themselves at Achashverosh’s party. Together, their actions saved the Jews from the decree against them.