The Book of Mormon teaches that there was a fall that “brought upon all mankind a spiritual death as well as a temporal, that is, they were cut off from the presence of the Lord” and that human beings became “carnal, sensual, and devilish, by nature” (Alma 42:9-10). The result is that the natural man is an enemy to God and has been from the fall of Adam (Mosiah 3:19).
The Book of Mormon also teaches that the fall was necessary for humanity. If there was no fall then Adam and Eve “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” (2 Nephi 2:22-23). Accordingly, “Adam fell that men might be” (2:25). If Adam had not sinned, then the human race would not have existed.
But since human beings are fallen and separated from God, they are also told how to be saved. Four components are essential to one securing salvation: faith, repentance, and baptism, and ongoing faithfulness; according to 2 Nephi,
“And he commandeth all men that they must repent, and be baptized in his name, having perfect faith in the Holy One of Israel, or they cannot be saved in the kingdom of God. And if they will not repent and believe in his name, and be baptized in his name, and endure to the end, they must be damned” (9:23-24).
According to Mosiah, those who remain faithful in their lives will have their sins forgiven and “are received into heaven, that thereby they may dwell with God in a state of never-ending happiness” (2:41).
In his later teaching, Joseph Smith added to the concept of salvation and the afterlife. For example, there are three stages post-death. In the first of the three stages post-death, there are one of two places a person’s spirit enters upon death: spirit paradise or spirit prison. Spirit paradise is for those who die righteous, and whose spirit will be “received into a state of happiness, which is called paradise, a state of rest, a state of peace, where they shall rest from all their troubles and from all care, and sorrow” (Alma 40:12).
Spirit prison is for those who “died in their sins, without a knowledge of the truth, or in transgression, having rejected the prophets” (Doctrine and Covenants 138:32). However, given the atoning work of Jesus, spirits have the opportunity to leave spirit prison and enter spirit paradise. Mormons believe that in spirit prison, spirits are taught by righteous spirits about faith in God, repentance, baptism, and other principles of Christ’s gospel. There will indeed be a day of judgment: “the day cometh that all shall rise from the dead and stand before God, and be judged according to their works” (Alma 11:41). The second stage of post-death judgment occurs after Jesus’ return to the Earth where he will judge the people.
There is a three-tiered hierarchy of heavens described by Joseph Smith. These are exaltation in the Celestial Kingdom for faithful Mormons where people may become gods or angels (Doctrine and Covenants 132:20), the Terrestrial Kingdom for righteous non-Mormons (Doctrine and Covenants 76:75-76), and the Telestial Kingdom for wicked and ungodly (not to be confused with hell) (Doctrine and Covenants 76:103-104). God exists in the Celestial Kingdom and to live with Him again for eternity people must accept the gospel of Jesus and live out its laws.