Heavenly Father sent us here to mortality so that we can gain the experience of living in mortality, which enables us to enjoy His blessings. Part of his perfect plan was that he would give us “agency” or the ability to choose and act for ourselves, (Joshua 24:15, Old Testament; 2 Nephi 2:26-29, Book of Mormon). Our progression in life depends on whether we choose to follow Jesus Christ, or follow the adversary.
Adam and Eve were given agency in the Garden of Eden, which they used when they chose to eat of the forbidden fruit, subjecting themselves to both physical and spiritual death; physical because they were able to die, and spiritual because they could no longer be in the presence of our Heavenly Father. We believe that the fall of man was part of God’s plan, as it was only after the fall that they could bare children and understand good and evil, thus enabling them to learn and progress, (Genesis 3, Old Testament; 2 Nephi 2:25, Book of Mormon; Alma 12:22-34, Book of Mormon). In our mortal position, we often yield to temptation, sin, and make mistakes. We cannot overcome the effects of sin by ourselves--we are helpless without the atonement of Jesus Christ.