Who made Purim a feast?

The chapter answers in its own words. "Mordecai wrote these things, and sent letters to all the Jews" (9:20), "to enjoin them that they should keep the fourteenth and fifteenth days of the month Adar yearly" (9:21). "The Jews accepted the custom that they had begun, as Mordecai had written to them" (9:23), and "the Jews established and imposed on themselves, on their descendants, and on all those who joined themselves to them" (9:27) that they would keep the two days (9:27-28). "Esther the queen, the daughter of Abihail, and Mordecai the Jew wrote with all authority to confirm this second letter of Purim" (9:29), and "The commandment of Esther confirmed these matters of Purim; and it was written in the book" (9:32). The chapter doesn't say that God commanded the days; like the rest of the book, it doesn't name God (see the introduction), and these notes don't add what it doesn't say. The letters speak of fasting as well as feasting: "in the matter of the fastings and their mourning" (9:31). The New Testament never names Purim (see the introduction).