Why did God allow humans to fall into sin? To answer that question, we need to think of redemption. If our redemption (and glorification) is merely a return to the garden-of-Eden-state, then the fall makes little sense (hardly the felix culpa it's known to be). On the other hand, if our redemption eventually brings us to a state that is better than our original state in Eden, the fall begins to make sense. In that way, the fall is a tool in the hands of the Redeemer... CLICK TO READ MORE.
5 Benefits of the Fall
The Fight of Faith 