According to Genesis, God planted the Tree of Knowledge of Good and Evil in the Garden of Eden, then commanded Adam not to eat it. God then created Eve, who knew about the command but decided to eat, in part because the tree would allow her to be wise and know good and evil; Adam then did the same, for reasons unexplained. Because man knew good and evil, God made him mortal and imposed other penalties: “And the Lord God said, ‘The man has now become like on of us, knowing good and evil. He must not be allowed to reach out his hand and take also from the tree of life and eat, and live forever.'”
So what is bad about man knowing good and evil? Should we not use our minds to consider right and wrong? A & E obviously had the concepts of good and evil beforehand, because the serpant made use of them in persuading Eve. We are also given to understand that they didn’t do evil before eating from the tree, perhaps because it hadn’t occurred to them. There is no indication that God gave them detailed commands on what not to do- the Ten Commandments come later. They seem to have known good and evil already.
I think the important distinction is between intuiting, reasoning, or otherwise figuring out an already existing right and wrong on the one hand, and creating a man-made morality for our own purposes on the other. It isn’t a question of using one’s mind versus blindly following God’s commands. Old Testament chronology implies what the New Testament states explicitly, that sin necessitated the Old Testament Law; God didn’t give man in the Garden lots of commands. And how we use our minds depends on whether we think there is a right and wrong independent of our inclinations.
There is nothing really wrong with eating from the Tree, as far as I can tell, except that God told Adam and Eve not to, and he seems to have told them not to because he didn’t want them to “know good and evil.” By making themselves authorities on right and wrong, Adam and Eve had already fallen, despite the fact that the action they took (eating the fruit) has no moral content apart from representing that very decision to make themselves authoritative.
Once Adam and Eve ate, “the eyes of both of them were opened, and they realized they were naked, so they sewed fig leaves together and made coverings for themselves.” This may be another hint as to how to interpret “know,” (comments would be most welcome from anyone who can read Genesis untranslated.) They know evil as a direct experience, a real possibility for themselves that they will from now on have to guard against.
Once they have known evil, God certainly doesn’t object to their putting clothes on; he endorses it. The genie can’t be put into the bottle, and one necessary and proper response to evil is to develop social conventions to mitigate its effects.
People talk about the Fall as the basis for man’s depraved nature, yet the story, I think, illustrates the complexity of human nature. We have a purpose, a natural good, a Summum bonum and what not, and a natural inclination to fall short of it. Our nature is to fall away from our natural good.
I briefly noted that God’s giving of the Law comes after the Fall, indicating that Adam and Eve already knew the right thing to do. Cain and Abel are of course our next pair, and would it be wrong to argue that God starts laying down the law here?
Though God had not so far as we know commanded any such thing, the brothers each made a sacrifice to God. God found Cain’s offering for some reason to be unsatisfactory. When Cain became angry, God said “If you do what is right, will you not be accepted? But if you do not do what is right, sin is crouching at your door; it desires to have you, but you must master it.”
Here again is the implication that Cain knows what is right, though no command has been given. Perhaps God has told Cain what was wrong with his sacrifice, but when God issues a command Genesis tends to make it clear. We also have the idea, similar to the story of the Serpent tempting Eve, that sin is an alien, unwelcome force seeking to ensnare us, but it is more a part of Cain than it was with Adam and Eve. Now there is no Serpent, and sin is working from within Cain himself. What we do with our sinful nature is from now on what will matter.
Cain also clearly knows it was wrong to murder Abel; his responses to the Lord on this point are evasive. This is despite the fact that God has not issued a command against murder. But his response, I think, moves toward such a law. He punishes Cain, because the blood of the murdered Abel cries out to him from the ground. He then marks Cain so that others will know not to kill him. Cain is punished and will be an outcast, but his punishment is itself then limited, and people may not take upon themselves to go beyond it.