Then what do you think the knowledge of good and evil is then?
If I may, there's been some pretty good speculation on this from the past. The knowledge of good and evil could be just
that, the literal knowledge, i.e.
experience, of good and evil, the very first experience of evil being the very sin that changed their whole state of being. Prior to that they had known only good, since everything in creation is good to begin with. But the experience of evil-including all sin/evil that would immediately follow in their brave new world, brought good into focus, and therefore into contrast. Prior to that loss of innocence there may not have even been a word for good, much less a concept of it since, again,
everything was good anyway. But now they had knowledge that God had: the reality of good and the reality of evil. Man continues to experience-or know-both to this day.
And this knowledge does have a benefit-that of helping us identify and choose between the two-to shun evil and run to the good like Prodigals who've grown weary of life away from the father, and so ultimately back to the Ultimate Good and source of all good: God, Himself, the good that Adam dismissed by denying His authority, and therefore His godhood.
Anyway, this theory aligns with the Hebrew word used for knowledge here, "yada", which is often used to denote this very idea: direct, intimate knowledge such as carnal knowledge, to
know one's mate in the intimate sense for example. The OT uses the word in that case and similarly in others here and there.
In any case, the act itself was the first act of disobedience of God, the equivalent of determining good and evil, right and wrong, for themselves, which is itself equivalent to them becoming their own "gods" for all practical purposes. And that's the world we find ourselves in today, a world where man's will effectively reigns -for better or worse but definitely for worse when it results in the sin that is so prevalent in our world.