“This is an entirely subversive promise. God knows good and evil with the knowledge of omniscience: he knows all that has been, all that is, all that will be, all that might be under different circumstances–he knows it all, including what evil is. But the woman is going to learn about evil by personal experience; she is going to learn about it by becoming evil.
An illustration may help. My wife is a cancer survivor. She is a fairly highrisk survivor, and so the doctors still watch her very closely. The oncologists know a great deal about the disease–from the outside. She knows cancer from the inside. God knows all there is to know about sin, but not by becoming a sinner. The woman will find out about the knowledge of good and evil from the inside. In that sense, what the serpent promises is a total lie.” -D.A. Carson