During the period between the first and second Jewish returns from Babylonian captivity (536 and 457 B.C.), many Hebrews remained in Persia. At that time, a dreadful plot to exterminate the Jews was instigated by a Persian official named Haman.
Esther, a beautiful Jewess, was raised up by God to be instrumental in the deliverance of her people (Esth. 4:14). She became the queen and, through her influence, Haman was destroyed, and the Hebrews were spared.
The book also explains the origin of the Jewish feast of Purim, a commemoration of the Jews' deliverance from Haman (9-10). An underlying theme is the preservation of the Hebrews in view of the coming Messiah.