Xerxes could not just abrogate his proclamation to destroy the Jews. Once his word had been given, written, and sealed with his ring, the command was bound to stand. The Jews would be attacked. But there was nothing to keep the Jews from being allowed to protect themselves.
You should have already noticed two things in this book: First, the Jews are hated. Second (though this is a little harder to see), why they are hated. Jews seem like a magical people, a force to be reckoned with. Notice that when Haman went home in disgrace, having spent the day honoring Mordecai, a man he despised, his family said to him: Since Mordecai, before whom your downfall has started, is of Jewish origin, you cannot stand against him” (note my emphasis).
Zechariah, who had prophesied just a few years before, plainly stated that God’s preference was for the Jews. “I will make Jerusalem an immovable rock for all the nations. All who try to move it will injure themselves. On that day I will strike every horse with panic and its rider with madness,” declares the Lord. “I will keep a watchful eye over the house of Judah, but I will blind all the horses of the nations” (Zechariah 13:3-4).
The Persians weren’t wrong to think God’s people were special – shielded by God’s power. That truth is being played out in the story of Esther. It’s just too bad that God’s people often overlook the real blessing of their relationship with our heavenly Father.