Why does it say "u'Ma'amar Esther Kiyam"?
Vilna Gaon: Due to her power, Divrei ha'Purim were fulfilled and written in a Sefer. She commanded and they were not allowed to nullify her words, like it says (Megilah 7a) that she sent to Chachamim to include Megilas Esther in Kesuvim. They needed to consent, because she was queen 1 .
Even a Jewish king, we need not obey his command to transgress the Torah (Sanhedrin 49a)! Perhaps they needed to consent because she saved everyone, just like Rachav's charge to save her family (Yehoshua 2:12-13) overrode "Lo Sechayeh Kol Neshamah" (Devarim 20:16), because she saved Yehoshua's spies. However, 'because she was queen' implies unlike this. (PF)
What is the significance of being called a "Sefer"?
Refer to 9:29:4:1.
Rashi: This shows that Chachamim of the generation consented to include Megilas Esther in Kesuvim.
