Heavenly Father caused Satan and his angels to come to earth, but because they will never receive bodies they were miserable. They have not forgotten the premortal life, and now they do all they can to destroy Heavenly Father's work and make us miserable like they are. Heavenly Father allows this because mankind cannot choose righteousness if they are not tempted by wickedness.
Thinking he could destroy Heavenly Father's plan, Satan came to the Garden of Eden to persuade Adam and Eve to eat from the fruit of the tree of good and evil. Satan approached Adam first and was refused, but Eve yielded to temptation and ate the fruit. Adam realized that this meant she would now have to leave the garden, and he chose to eat the fruit as well so that he and Eve could stay together.
Some Christians condemn Eve for this act, but we should honor her wisdom and courage, for it was through her act of transgressing one of Heavenly Father's commands that Adam and Eve became mortals and allowed the rest of us to have mortal lives as well. Satan's diabolical efforts at destruction unwittingly furthered Heavenly Father's plan for mankind, allowing them to progress on their path toward Godhood.
Adam and Eve's bodies changed after eating the fruit. As mortals they could now have children, but they were also able to become sick, feel pain and sorrow, and one day they would die. Heavenly Father also changed the entire earth, and all other living things became mortal as well. Adam and Eve were then driven out of the Garden of Eden and into the lone and dreary world.
• Gospel Fundamentals, (2002), Chapter 5: Jesus Made the Earth, Part Two: Leaving the Presence of God
• Old Testament Student Manual Genesis-2 Samuel, (1980), 38–43
• The Pearl of Great Price Student Manual, (2000), 3–27
• Hamula, James, J. “Hearken to the Voice of the Lord”. Pacific Area Message, June 2013.
Traveling about 90 miles northeast from the Garden of Eden, Adam and Eve settled at a place called Adam-ondi-Ahman which is in modern-day Daviess County, Missouri. Now when Heavenly Father told Adam and Eve that they would die the day they ate the fruit of the tree of the knowledge of good and evil, he meant a day according to time on Kolob, where one day is 1,000 Earth years.
Adam and Eve began tilling the soil and raising flocks for a living. Sometimes they were happy, other times sad. In obedience to Heavenly Father's command, they had many children. Their children began to marry each other and start families of their own, and thus bodies began to be provided for Heavenly Father's spirit children to live mortal lives on Earth.
The First Christians
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Also from the creator of The Brick Book of Mormon: