Esther 9:26

Wherefore they called these days Purim after the name Pur. This first על־כּן refers to what precedes and states the reason, resulting from what has just been mentioned, why this festival received the name of Purim. With the second על־כּן begins a new sentence which reaches to Est 9:28, and explains how it happened that these feast-days became a general observance with all Jews; namely, that because of all the words of this letter (of Mordochai, Est 9:20), and of what they had seen concerning the matter (על־כּכה, concerning so and so), and what had come upon them (therefore for two reasons: (1) because of the written injunction of Mordochai; and (2) because they had themselves experienced this event), the Jews established, and took upon themselves, their descendants, and all who should join themselves unto them (proselytes), so that it should not fail (i.e., inviolably), to keep (to celebrate) these two days according to the writing concerning them and the time appointed thereby year by year.

We left two royal edicts in force, both given at the court of Shushan, one bearing date the thirteenth day of the first month, appointing that on the thirteenth day of the twelfth month then next ensuing all the Jews should be killed; another bearing date the twenty-third day of the third month, empowering the Jews, on the day appointed for their slaughter, to draw the sword in their own defence and make their part good against their enemies as well as they could. Great expectation there was, no doubt, of this day, and the issue of it. The Jews' cause was to be tried by battle and the day was fixed for the combat by authority. Their enemies resolved not to lose the advantages given them by the first edict, in hope to overpower them by numbers; the Jews relied on the goodness of their God and the justice of their cause, and resolved to make their utmost efforts against their enemies. The day comes at length; and here we are told, I. What a glorious day it was, that year, to the Jews, and the two days following - a day of victory and triumph, both in the city Shushan and in all the rest of the king's provinces (v. 1-19). II. What a memorable day it was made to posterity, by an annual feast, in commemoration of this great deliverance, called "the feast of Purim," (Est 9:20-32).

9:26-28 This paragraph justifies Purim as an approved Jewish festival even though Moses did not authorize it along with other festival days.