[Ester]

Neither the bible nor its author are contradictory. In order to understand the origin of sin, you must first acknowledge that the "tree of knowledge" was not a literal tree. Consider the usage of the word "know" in the bible: for example in Gen. 4:1, " And Adam knew his wife, and she conceived and bare a son etc.." Here, the word know is synonymous with sex.
The beguiling of Eve by the serpent (who by the way walked uprightly before the curse), and Eve's partaking of the "fruit", is symbolic for the sexual relationship between Eve and the serpent.

I would have liked to go deeper with this topic; unfortunately, I do not have much time at the moment.