What did they not have before eating of the fruit of the Tree?
They did not have the Knowledge of Good and Evil. They were unable to determine if something was right or wrong. If they were able to do that, then, they already would have KNOWN about right and wrong.
They might have been told, but without understanding of the consequences.
They had the ability to do wrong. Just not the knowledge to know if what they did was wrong or not.
In other words, god set them up. If man did not begin to know the difference between right and wrong, man would have been forever like that animals. It is that knowlege that brings man closer to god, by giving him a choice to life a sanctified life by choosing good over evil.