Because Haman the son of Hammedatha, the Agagite, the enemy of
all the Jews, had devised against the Jews to destroy them
Had formed a design to exterminate them from the whole Persian empire in one day:
and had cast Pur, (that is, the lot,) to consume them, and to destroy
them;
had cast lots to find out what would be the most lucky day in the year for him to do it on, and the most unlucky and unfortunate to the Jews; and, according to the lot, the thirteenth of Adar was pitched upon; this and the following verse give the reasons for observing the above two days as festivals.