Martin Q. Blank said:
Esther doesn't seem that "Biblical". No mention of God. Story of revenge. It's more of a historical telling of how the holiday of Purim originated. It seems similar to the other apocrypha books. Only book not found in the dead sea scrolls. When and why was it included in the scriptural canon?
Pesherim commentaries on the text of Esther were at Qumran, among the Dead Sea scrolls. The Esther text does some interesting stuff in the original Hebrew, such as mystically interpreting the Persian Kings palace as God's new temple. The text foretells the destruction of both the first and second temple, which hints at the fall of Persia.