22 And now, behold, if Adam had not transgressed he would not have fallen, but he would have remained in the garden of Eden. And all things which were created must have remained in the same state in which they were after they were created; and they must have remained forever, and had no end.If Adam had not transgressed, he would not have fallen. If it was the transgression that caused the Fall, then it makes sense that God would give a commandment that Adam could choose to disobey in order to trigger its consequences. Elder Dallin H. Oaks has said:
23 And they would have had no children; wherefore they would have remained in a state of innocence, having no joy, for they knew no misery; doing no good, for they knew no sin.
24 But behold, all things have been done in the wisdom of him who knoweth all things.
25 Adam fell that men might be; and men are, that they might have joy.
"Some acts, like murder, are crimes because they are inherently wrong. Other acts, like operating without a license, are crimes only because they are legally prohibited. Under these distinctions, the act that produced the Fall was not a sin—inherently wrong—but a transgression—wrong because it was formally prohibited. These words are not always used to denote something different, but this distinction seems meaningful in the circumstances of the Fall."Partaking of the forbidden fruit was not evil, but it was nevertheless a transgression because it was forbidden. If Adam had not transgressed this commandment of the Lord, everything in the garden would have remained in the same state forever. While it is true that there was no sorrow in the garden, it must also be true that there was no joy in the garden. Adam was unable to commit sin in the garden, but that also made him incapable of being righteous. For this reason, his entire existence in the Garden was meaningless except for one thing: he needed to bring about the Fall of man through his transgression of God's commandment. Partaking of the fruit was the only meaningful thing that he could do in the garden in terms of his spiritual progression.
The Fall had many consequences, but I think that it is fair to say that (because of the Atonement) the positive consequences far outweigh the negative ones. Possibly the greatest positive consequence was that Adam and Eve were now able to have children. Without the Fall, none of us would have had the chance to enter into this mortal life and take part in the great plan of happiness.
It is important to remember though that without the Atonement, the plan of happiness would not have had a happy ending for any of us. It is impossible to completely understand the Fall without a knowledge of the Atonement. Likewise, it is impossible to understand the Atonement without putting it into the context of the Fall. The two doctrines are complementary, and they literally inseparable.