"So the Jews agreed to continue the celebration they had begun, doing what Mordecai had written to them. For Haman son of Hammedatha, the Agagite, the enemy of all the Jews, had plotted against the Jews to destroy them and had cast the pur (that is, the lot) for their ruin and destruction. But when the plot came to the king's attention, he issued written orders that the evil scheme Haman had devised against the Jews should come back on his own head, and that he and his sons should be hanged on the gallows. (Therefore these days were called Purim, from the word pur.)" NIV translation
So, this became a national Jewish holy day celebrating the deliverance of God's people from death at the hands of their enemy. This was a time to remember how God had saved them and it is a picture of how we are saved from our own death penalty through the blood of Jesus Christ. The celebration was (and still is today) called Purim from the word pur for lot.
"Because of everything written in this letter and because of what they had seen and what had happened to them, the Jews took it upon themselves to establish the custom that they and their descendants and all who join them should without fail observe these two days every year, in the way prescribed and at the time appointed. These days should be remembered and observed in every generation by every family, and in every province and in every city. And these days of Purim should never cease to be celebrated by the Jews, nor should the memory of them die out among their descendants." NIV translation
We see, from this passage, the establishment of the Feast of Purim which is celebrated by Jews even today.
We notice that this custom was established by the people and not directly prescribed by God. This is a very good tradition as it reminds God's people of His hand of deliverance but we must remember that it is still a tradition.
There are many traditions in the church of today and often these traditions cause division and splits among the believers. That is the reason for so many denominations and why we must remember the difference between man's traditions and God's instructions.
"So Queen Esther, daughter of Abihail, along with Mordecai the Jew, wrote with full authority to confirm this second letter concerning Purim. And Mordecai sent letters to all the Jews in the 127 provinces of the kingdom of Xerxes - words of goodwill and assurance - to establish these days of Purim at their designated times, as Mordecai the Jew and Queen Esther had decreed for them, and as they had established for themselves and their descendants in regard to their times of fasting and lamentation. Esther's decree confirmed these regulations about Purim, and it is written down in the records." NIV translation
This Feast of Purim became the law of the land by this political order.