I don't believe in the fundamentalist Christian theory of how the Tree of Knowledge story supposedly played out. It sounds as if you don't, either. But I don't think it's totally nonsense, just partly so.
As the story of Adam & Eve and the garden is related by literal-minded Christians, it's implausible. It also makes God sound very strange indeed.
However, Fireball offers a good, conventional, "Christian" interpretation that works in practical human terms, if not theological ones.
For humans to have "free will," we must be able to do things that God and/or other humans don't like. In some sense, we must have the ability (a) to disobey God and (b) to choose evil rather than good; otherwise, we really are robots.
Therefore I look on the Genesis story as a kind of parable about what every human being has to do to develop an independent personality. We have to rebel, have to act selfishly & arbitrarily & foolishly; otherwise we are very weak.
I get this idea from the philosopher Hegel, who makes "negativity" (what Christians might call "sin") the basic source of all human intellectual development from the dawn of history on.
However, I also think the idea of Adam and Eve disobeying God to demonstrate their free will is a bit like the psychological concept of the "terrible twos," the age at which the child becomes an independent person partly by saying "no, no, no" to every suggestion of the parents.
By disobeying God & eating from the wrong tree, I think Adam & Eve experienced their "terrible twos" and took a necessary step forward in human development -- and in * knowledge* of good and evil, in itself a good thing.
But of course, there are some psychological costs to that step. Once you have disobeyed either God or Mommy and recognized that you can act as you choose, you've entered a much less innocent existence. And you can't return to an innocent state again, no matter how you try, for angels with flaming swords block your way.
Other than that, I think the Genesis story, as its name implies, is basically an "origins" myth. That is, it's a fanciful attempt to explain how the world came to be as it is.
The story of the Garden, for instance, attempts to explain the origins of (a) death (b) sexual shame (c) the pains women experience in childbirth, (d) the burden that physical labor imposes on men, and even (e) why snakes have no legs.
Moving on to Joshua -- this is crude and bloody tribalism justified in the name of religion, I think.
BTW, some modern Jewish archaeologists argue that some of the genocide portrayed in Joshua never really happened.
They say the early Jews, for all their claims to the contrary, were really a subset of the Canaanites, and they argue that the Joshua story was made up by one group of ex-Canaanites with "Jewish" beliefs to justify and explain their antagonism towards another group of Canaanites with "idolatrous" beliefs.
3. The concepts of life after death, divine judgment, and the prospects of heaven & hell are concepts that Judaism developed many centuries after the origin myths in Genesis.
I had a brilliant Jewish philosophy professor in college, probably a skeptic in religion, who argued that the Jews started to talk about Heaven, Hell & Judgment only after it became apparent that God's justice often goes unfulfilled among mortal men on earth.
The Book of Job is pivotal in terms of the logical shift involved, my professor thought. He noted that the 5 books of Moses basically promise that if people live correctly and sacrifice to God, God will reward them for this.
The big problem that Job confronts, however, is that he, whom even God considers a good man, is given over to Satan to be tormented for no justifiable reason. Meanwhile wicked men who openly flout God's laws are being allowed to prosper, despite their impiety.
Job offers a startlingly realistic picture of how the world actually is, my professor thought: it's very "modern" in that way. But this picture is fatal to Jewish belief in God rewarding those who serve him -- unless, that is, divine punishments and rewards can somehow be transferred from this world to the next.
Once we introduce the idea of Hell, we can comfort ourselves with the idea that bad people will be punished in Hell, even though they appear to succeed here on earth.
Put these three insights together, and I think you can explain much of what seems contradictory in Judaeo-Christian scriptures. I think the key lies in recognizing that whether God changed or not, people's ideas about God shifted over time, and the Bible records those shifts.
-- A friendly agnostic