The Fall Was a Necessary Event in God’s Plan of Happiness

2 Nephi 2:22–24

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.
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.

Elder John A. Widtsoe said:

“Such was the problem before our first parents: to remain forever at selfish ease in the Garden of Eden, or to face unselfishly tribulation and death, in bringing to pass the purposes of the Lord for a host of waiting spirit children. They chose the latter. This they did with open eyes and minds as to consequences. The memory of their former estates may have been dimmed, but the gospel had been taught them during their sojourn in the Garden of Eden. They could not have been left in complete ignorance of the purpose of their creation.”

(Evidences and Reconciliations, arr. G. Homer Durham, 3 vols. in 1 [1960], 193–94.)