One thing the Jews don't do is to plunder the Amalekites in 9v10 + 9v15. King Saul was reprimanded in 1 Samuel 15v19 for having done this, seeking to keep the Amalekites possession for himself instead of thoroughly destroying them. The Jews do not fall into his error, their enemy is vanquished.
So, they celebrate in style. The celebration is called Purim in memory of Haman's confidence in the Pur (lots) for his victory over the Jews. The title is ironic for the Jews. Haman believed that chance had fallen in his favour to defeat the Jews he so despised. But his plot returned upon himself. And the Jews rejoice.
As the book concludes it is Mordecai the Jew not Haman the Amalekite who is Prime Minister. Xerxes remains a questionable monarch, prepared to immediately bestow all of Haman's benefits on Mordecai - you'd think he'd become a bit more cautious!
The promises of God await their fulfillemnt but they know afresh the certainty of God's deliverance. As Esther draws to it's close we should rejoice. We know the great victory of God over his enemies. All God's promises there fulfilled. The Cross of Christ, God's great and final answer to his promises. The great YES!
"And on that final day, the citizens of heaven