[Bloody Sam Roberts]

Thus Eve could then say to the serpent (Satan) that he was a liar and that there was another reason for this particular tree

And that was so Eve could see the serpent for what he was. Evil.
Without that ability, the lord of lies could easily have said that he was of God and she must do as he says. She never would have known the difference.
The Lord our God knew this and thus did he create the Tree of Knowledge.

[Laissez-faire capitalist]

If Satan had said that He was of God and that she must do as he says, all she would have to have done is say to him the following:

“God will show up “in the cool of the evening” to walk with Adam as He always does. We will wait until then to ask God what he has to say about what you (the serpent) are saying. Then we will know if there is any difference in what you and He are saying and have said.”

And then she could turn back to her original point: “If what you (the serpent) is saying is true, then why did God create the tree in the first place?”

[sportutegrl]

Why is Eve punished for doing evil, before she eats of the fruit of knowledge? She didn't know she was doing wrong until she took a bite.