Esther is a complex figure, but basically she incarnates the Jewish people.
The Jewish people is always described in the Bible as having the characteristics of a woman.
Sometimes the allusion is purely mystical–for example, in the Song of Songs.
But aside from mysticism, the recurrent image in the language of the Prophets is that of the bride, companion, wife of God.
Marital symbolism, as found in Hosea, Isaiah, Jeremiah, and Ezekiel, is one of the most striking features of biblical prophecy.
It has its roots in what the mystics would later call Knesset Israel, the community of Israel, the mystical unification of the source of Jewish souls, which collectively forms the interlocutor and the "wife" of the Divinity.
The entire history of the world can be seen as a marital relationship, a more or less successful marriage of love (depending on the era) between God and Israel.
–Rabbi Adin Steinsaltz
From The Seven Lights by Rabbi Adin Steinsaltz