The Persian King, Xerxes (Ahasuerus), who reigned over a mighty empire, decided to give a 7-day banquet for all the people present in Susa, the capital city.  On the last day of the banquet he asked his wife, Queen Vashti, to come to the banquet so his guests could enjoy her beauty.  She refused, Xerxes deposed her and the search was on for a replacement. Xerxes promoted one of his princes, Haman, above all the other princes and ordered the king’s servants to bow to him.  

When Esther’s uncle Mordecai refused to bow down to pay obeisance, Haman went berserk and plotted to convince King Xerxes to annihilate all Jews, young and old, women and children.  Esther was in a position to petition and influence the king on behalf of her people.  However, there was a major problem: no one could approach the king without permission.  Mordecai convinced Esther to go to the king anyway. Risking the death penalty, Esther consented and called for a fast. Just like King Jehoshaphat of Judah in (2 Chronicles 20:4). 

The three days of fasting by Esther and the Jews, was a national rallying cry for salvation. The whole nation united behind Esther, and God indeed answered their prayers. God indeed responds to the cry of his people if it is done from a pure and sincere heart.