Only the King could save the Jewish people and that only by issuing another decree.  Esther had to talk to the King.  To prepare for this meeting Esther asked all the Jews to fast.  In commemoration of that fast many people today still fast the day before Purim praying for God’s continual preservation of Israel. 

Esther 4:15-17

Then Esther told them to reply to Mordecai: “Go, gather all the Jews who are present in Shushan, and fast for me; neither eat nor drink for three days, night or day. My maids and I will fast likewise. And so I will go to the king, which is against the law; and if I perish, I perish!”

So Mordecai went his way and did according to all that Esther commanded ^[b]him.

PRAY FOR ISRAEL TO RELY ON FASTING AND PRAYER AND NOT HER OWN STRENGTH.