A Commentary, Critical, Practical, and Explanatory on the Old and New Testaments, by Robert Jamieson, A.R. Fausset and David Brown  at sacred-texts.com
est 9:1THE JEWS SLAY THEIR ENEMIES WITH THE TEN SONS OF HAMAN. (Est. 9:1-19)
in the twelfth month, . . . on the thirteenth day of the same--This was the day which Haman's superstitious advisers had led him to select as the most fortunate for the execution of his exterminating scheme against the Jews [Est 3:7].
est 9:2The Jews gathered themselves . . . no man could withstand them--The tables were now turned in their favor; and though their enemies made their long meditated attack, the Jews were not only at liberty to act on the defensive, but through the powerful influence enlisted on their side at court together with the blessing of God, they were everywhere victorious.
the fear of them fell upon all people--This impression arose not alone from the consciousness of the all-powerful vizier being their countryman, but from the hand of God appearing so visibly interposed to effect their strange and unexpected deliverance.
est 9:5Thus the Jews smote all their enemies--The effect of the two antagonistic decrees was, in the meantime, to raise a fierce and bloody war between the Jews and their enemies throughout the Persian empire; but through the dread of Esther and Mordecai, the provincial governors universally favored their cause, so that their enemies fell in great numbers.
est 9:13let it be granted to the Jews which are in Shushan to do to-morrow also according unto this day's decree--Their enemies adroitly concealing themselves for the first day might have returned on the next, when they imagined that the privilege of the Jews was expired; so that that people would have been surprised and slain. The extension of the decree to another day at the queen's special desire has exposed her to the charge of being actuated by a cruel and vindictive disposition. But her conduct in making this request is capable of full vindication, on the ground (1) that Haman's sons having taken a prominent part in avenging their father's fall, and having been previously slain in the melee, the order for the exposure of their dead bodies on the gallows was only intended to brand them with public infamy for their malice and hatred to the Jews; and (2) the anti-Jewish party having, in all probability, been instigated through the arts or influence of Haman to acts of spiteful and wanton oppression, the existing state of feeling among the natives required some vigorous and decisive measure to prevent the outbreak of future aggressions. The very circumstances of their slaying 800 eight hundred Jews in the immediate vicinity of the court (v. 6, 15) is a proof of the daring energy and deep-rooted malice by which multidues were actuated against the Jews. To order an extension, therefore, of the permissive edict to the Jews to defend themselves, was perhaps no more than affording an opportunity for their enemies to be publicly known. Though it led to so awful a slaughter of seventy-five thousand of their enemies, there is reason to believe that these were chiefly Amalekites, in the fall of whom on this occasion, the prophecies (Exo 17:14, 16; Deu 25:19) against that doomed race were accomplished.
est 9:19a day of . . . feasting . . . of sending portions one to another--The princes and people of the East not only invite their friends to feasts, but it is their custom to send a portion of the banquet to those who cannot well come to it, especially their relations, and those who are detained at home in a state of sorrow or distress.
est 9:20THE TWO DAYS OF PURIM MADE FESTIVAL. (Est 9:20-32)
Mordecai wrote these things--Commentators are not agreed what is particularly meant by "these things"; whether the letters following, or an account of these marvellous events to be preserved in the families of the Jewish people, and transmitted from one generation to another.
est 9:26they called these days Purim after the name of Pur--"Pur," in the Persian language, signifies "lot"; and the feast of Purim, or lots, has a reference to the time having been pitched upon by Haman through the decision of the lot. In consequence of the signal national deliverance which divine providence gave them from the infamous machinations of Haman, Mordecai ordered the Jews to commemorate that event by an anniversary festival, which was to last for two days, in accordance with the two days' war of defense they had to maintain. There was a slight difference in the time of this festival; for the Jews in the provinces, having defended themselves against their enemies on the thirteenth, devoted the fourteenth to festivity; whereas their brethren in Shushan, having extended that work over two days, did not observe their thanksgiving feast till the fifteenth. But this was remedied by authority, which fixed the fourteenth and fifteenth of Adar. It became a season of sunny memories to the universal body of the Jews; and, by the letters of Mordecai, dispersed through all parts of the Persian empire, it was established as an annual feast, the celebration of which is kept up still. On both days of the feast, the modern Jews read over the Megillah or Book of Esther in their synagogues. The copy read must not be printed, but written on vellum in the form of a roll; and the names of the ten sons of Haman are written on it a peculiar manner, being ranged, they say, like so many bodies on a gibbet. The reader must pronounce all these names in one breath. Whenever Haman's name is pronounced, they make a terrible noise in the synagogue. Some drum with their feet on the floor, and the boys have mallets with which they knock and make a noise. They prepare themselves for their carnival by a previous fast, which should continue three days, in imitation of Esther's; but they have mostly reduced it to one day [JENNINGS, Jewish Antiquities].