Memuchan was the last and lowest of the advisors. Why did he speak first?
Torah Temimah citing Megilah 12b: This shows that the commoner jumps to the top 1 .
Vilna Gaon: Do not say that others spoke first, just his words are mentioned, for they were accepted. "Lifnei ha'Melech veha'Sarim' teaches that he spoke before them. It is extra. Obviously he spoke in front of them!
What is "Avsah"?
Rashi: She sinned.
Why did Memuchan say "Vashti ha'Malkah"> The king said "ba'Malkah Vashti"?
Malbim: She is not intrinsically a queen. She is queen only via the king. She must be judged like a commoner who rebelled against the king.
Why did he say that she sinned against all the Sarim?
Vilna Gaon: He did not mean that had she sinned only against the king, he would not be concerned. Really, her sin against the king was greatest! Rather, he saw that if the Sarim will judge her, they will not kill her, for this is like the king's desire. Also, they will flatter her. Also Memuchan (Haman) married a woman greater than himself, and wanted to expel her. Shamayim caused that Haman himself prepare the salvation! He wanted the king himself to judge her 1 . He could not pardon her, due to fear of the Sarim. Therefore, Memuchan said that she sinned against the Sarim! They are involved parties, so they cannot judge her, rather, the king will.
Malbim: Memuchan saw that the king wanted to judge her like between a man and his wife, and not as an affront to the king's honor, which is the Medinah's honor. The king also wanted to conceal it. Memuchan said that she belittled the honor of Achashverosh's kingship, which should be unlimited, since it was via conquest. She said that his kingship is via her; if so, it is limited. This pertains to the entire kingship!
Divrei Eliyahu: It is written in the laws of Paras and Madai that if the king judges, the verdict cannot be retracted. "Yetzei Devar Malchus mi'Lefanav v'Yikasev b'Dasei Faras u'Madai v'Lo Ya'avor" (19) - if a royal matter will come [from in front of him], surely it will not be annulled. Even though he cannot judge her sin against him, he can judge her sin against the Sarim.
How did she sin against the Amim?
Vilna Gaon: Later, they will hear.
Malbim: She will cause all wives to disgrace their husbands (17).
