Just as God the Father, Jesus Christ, and the Holy Ghost are one in purpose but three distinct beings, so the pillars of the gospel share a like similitude. Although we view the atonement as the center and core of our religion, without the fall, there is no atonement.
Adam’s fall brought about temporal and spiritual death and from this death all must be ransomed. The ransoming act must be carried out by a person without sin and He must be known to all creations. (This is the primary source of God’s power; see D&C 29:36).