Purim Tanit Esther - 11 Adar (Fasting Celebrated in Shushan or walled cities)
Purim - 14 Adar (Family Feast and gift giving to the poor day)
Shushan Purim - 15 Adar (Community Celebration, Celebrated outside Shushan or in rural areas)
The Amalekites began warring against God's people during Israel's journey up from Egypt. They continued to fight Israel throughout Amalekite history. God had (raised up and) given Saul the commandment to utterly destroy every last Amalekite and even their animals and everything that belonged to them, but Saul's pride would not obey. He and his men spared Agag, the king and the best of the sheep and cattle. They independently decided that surely God really meant the best of this plunder must not be destroyed. As a result of this terribly bad choice, God was grieved that he had made Saul king over Israel. Saul sought to excuse his disobedience through justifying it with sacrificial and ceremonial purposes, or "religiosity" but Samuel saw through his treachery and labeled this kind of disobedience what it really is: "To obey is better than sacrifice, and to heed is better than the fat of rams. For rebellion is like the sin of witchcraft arrogance and stubbornness is like the evil of idolatry."
(1 Samuel 15)
The consequences of Saul's disobedience caused immeasurable suffering through years of warring with the descendants of Amalekites for the children of Israel over the next 620 years. The attempted Holocaust in the book of Esther was yet another result of Saul's disobedience. Chapter 3 of Esther tells us Haman was a descendant of Agag. Chapter 9 tells us Esther finally does not hesitate to fulfill the commandment of the Lord by putting an end to all these Amalekites and also she deliberately did not lay her hand to that plunder.
The Purim (casting of lots) is an annual celebration for all Jews, as told in the book of Esther chapter 9:20-28 (NIV). Mordecai recorded these events, and he sent letters to all the Jews throughout the provinces of King Xerxes, near and far, to have them celebrate annually the fourteenth and fifteenth days of the month of Adar as the time when the Jews got relief from their enemies, and as the month when their sorrow was turned into joy and their mourning into a day of celebration.
He wrote them to observe the days as days of feasting and joy and giving presents of food to one another and gifts to the poor. 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 onto 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.)
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.
This is a very festive joyous celebration. Some women plant pots of barley so they can be mature for Habikkurim during the Feast of Unleavened Bread celebration.