After The Fall, man became carnal, sensual, and devilish by nature, indulging in lewdness, overt sexuality, and promiscuity. Although Adam and Eve taught their children the gospel of Jesus Christ, Satan came among them and said, "I, too, am a son of God." He convinced them to reject the gospel and to love him more than Heavenly Father. These sons and daughters of Adam and Eve became enemies of God.
Cain and Abel were sons of Adam who had both received the priesthood. But Cain rebelled from the gospel and came to love Satan more than Heavenly Father. Cain was the first man on Earth to enter into a covenant with Satan, plotting that if he killed his brother Abel, it would not become known to the world. "I will murder and get gain," said Cain, reveling in his wickedness.
Cain went out into the field with his brother Abel. They argued and then Cain rose up and killed Abel. Cain gloried in what he'd done, saying, "I am free! Surely my brother's flocks will now be mine." Thus Cain became like Satan and the sons and daughters of Heavenly Father who had rebelled with him in heaven: he had given himself completely over to wickedness and had no hope whatsoever of being saved.
Adam and Eve suffered extreme anguish and grief over what Cain had done. Now, it is for a wise purpose that Heavenly Father allows the wicked to exercise their agency, and this will be the case for as long as Satan has any influence over the hearts of men. Abel, having died a righteous man, has become an angel of Heavenly Father who received his body from the dead.
A hundred and thirty years after leaving the Garden of Eden, Adam and Eve had another son who they named Seth. When Seth was 69 years old, he was ordained into the priesthood. He was a perfect man, and his appearance was just like that of Adam his father. Adam and Seth were the two most handsome men to ever live.
Adam taught his family to read and write, and they kept a book of remembrance containing a genealogical record, what Heavenly Father had revealed about himself, the Plan of Salvation, the coming of Jesus Christ, and the inspired writing of Adam's family members. It was written in the pure and undefiled language of Adam.
The works of darkness on Earth began with Cain's descendants who were wicked and loved Satan more than Heavenly Father. And so both the gospel of Jesus and the works of darkness began to spread throughout the people. Satan and his angels laughed and rejoiced at the wickedness of Heavenly Father's children.