God had to tell Adam what to do and what not to do.  God had to show Adam what is and is not permissible.  God had to reveal to Adam that which is Good for Life and that which is Deadly to Life.  Adam did not have the ability to discern this through his own sensibilities.

Have you ever told someone that the world does not revolve around them?  It is natural for us to become self-absorbed in our own created false realities.  The point is we cannot trust our own derived reality.  So how do we know what reality is?