** WARNING -- Soapbox moment coming up... **
That question is one that many a religious scholar has grappled with.
My wife struggles with that concept probably the most in terms of her faith. Why couldn't God just have created us without the propensity to sin? Why all this apple in Eden, need to send a redeemer, fallible mankind stuff?!?!? Life would sure be alot easier without all that crap...
In order for Adam and Eve to understand their relationshop to God, they had to understand the concept of
obedience. If there were no limits imposed by God upon Adam and Eve, they would not have understood that concept nor would they have understood their relationship with God.
Look at it this way -- ever see a spoiled brat and how that brat behaves with his parents? Everything is allowed for this brat, and he has no respect for his parents or other people. Compare that with a child who is nutured and properly disciplined -- and you will see such a child has a far better outlook in life, and a better chance of succeeding as well. Such a child won't be perfect, but will better understand what is right and wrong, and learning that concept sooner in life can make a huge difference. (Yes, I am generalizing, and there are exceptions to the rule, but the concept is the same for the most part.)
While God did create man in his image, He didn't create them perfect. Why? I think God didn't want mankind to simply worship him without mind -- He wanted mankind to have a choice - to worship Him and follow His ways, or to abandon Him. That choice makes our relationship with God more dynamic. The option is ours to follow Him or not.
What does that give God? Well, without that freedom He gave us, we might as well all be robots. You can't really have much of a dynamic relationship with a robot... Despite man's fallibility, he also has the ability to worship God, and go against his human (sinful) nature and do the right thing. And that, it a nutshell, is what God get's jazzed up about -- when we in our limited nature are able to choose to do right and follow Him. Without the apple and the devil, this would not be.
Ok, I'll get off my soapbox now...
-Z-man.