2 Nephi

Everthing must have an opposite, because all existence is dependent on opposition. In minds like ours that are shaped by language and draw lines between things in order to distinguish and understand them, we would never comprehend right without wrong, or good without bad—and we would never see that the opposite of misery is holiness. Without opposites, everything would be just one big ball of being, and our brains wouldn't be able to sort through it. There would be no real life in this reality, no real consciousness, and no real joy. Things would be created, but to no end. They would exist, but would not truly be. And we would never have access to God's power and justice and mercy, we could never see who He is and what we are, we could never become like Him.

So, because everything needs an opposite, we needed a law—because there had to be sin so there could be obedience and righteousness. We had to be able to see the two things to know that holiness is happiness. Without law and pain and disobedience and punishment, we would never pick up on the natural connections—our brains would not allow us to learn that joy comes through goodness. We would never learn God—which would mean that we would never learn ourselves, and we would never learn the world, because all of these things are intertwined, all of creation sings and breathes together. Without one, none are.

This is what the Eden story is about. It's about the creation of opposites, of the necessity of choosing—and, if there is a choice, then there must be choices, and if it is to be a true choice, both choices must have real things to offer. So God gave Adam and Eve Eden and the Tree of Life, which was safe and beautiful, but which could not be understood in and of itself; and He gave them the Tree of Good and Evil, which is to say good and evil and everything that exists between the two. There was Eden, and then there was experience.

There's a snake in this story, and I think the snake is a fallen angel who has made it his purpose to tempt humanity. He wanted misery the way God wanted joy—and both were contained in the forbidden fruit. So he told Eve the truth: that eating the forbidden fruit would make her more like God, would open her eyes to what the world was. (He didn't tell her that it would lead to heartache and misery, that she would watch her son murder her son, that generations of her posterity would take their anger about her choice out on her daughters. He didn't tell her that, but he wasn't lying when he said that choosing reality could make her like God.) Eve and Adam chose the tree of experience, and they had to leave the garden to go where the experience was. They spent their lives working hard and having kids and feeling pain—but also watching things grow and knowing they'd been a part of it and having kids and feeling joy. None of that could have happened in Eden, and it needed to happen because innocent was not the best thing they could be.

Life became a time of repentance, which is to say, change with God. God commanded Adam and Eve and all who came after that they allow their experiences to change them, and that as they changed they spoke to God and allowed Him to shape that change, allowed Him to make them more than they were. Change is what couldn't happen in the Garden, and it's what would eventually allow them to both be like God and be with God. 

Humanity fell, and that could have been the end—but God knows everything and His hand is over everything and even what seems like the most enormous of disasters will eventually work for the good of them that love God. Eve and Adam fell so that humanity could truly live, and humanity truly lives so that they can have joy.