The Plan of Salvation: The Spirit World
Death is the portal to the remainder of eternity, after “premortal existence” and life on earth. At death, the spirit leaves the body and goes to a place called “the Spirit World,” where he or she awaits resurrection and judgment. (A resurrection of the righteous occurred when Christ was resurrected, and another resurrection of the righteous will occur at His Second Coming. Another resurrection will follow, and finally a resurrection of the wicked will occur after the Millennium.)
Even before the fall of Adam, which ushered death into this world, our Heavenly Father had prepared a place for the spirits who would eventually depart this mortal life. At the time of Jesus’ death, the spirit world was occupied by hosts of our Father’s children who had died—from Adam’s posterity to the death of Jesus—both the righteous and the wicked.
There were two grand divisions in the world of spirits. Spirits of the righteous (the just) had gone to paradise, a state of happiness, peace, and restful work. The spirits of the wicked (the unjust) had gone to prison, a state of darkness and misery. (See Alma 40:12–15.) Jesus went only to the righteous—to paradise—to teach the gospel to those who had departed. This visit took place after Christ’s crucifixion and before His resurrection.
Following is a portion of the glorious Vision of the Redemption of the Dead given to President Joseph F. Smith and sustained and accepted by the Church as holy scripture in April 1976:
“Their countenances shone, and the radiance from the presence of the Lord rested upon them, and they sang praises unto his holy name.” (Doctrine and Covenants 138:12–16, 18–19, 23–24.)
Jesus did not go to the wicked, or to prison. They were those who were unrepentant and who “had defiled themselves while in the flesh.” (Doctrine and Covenants 138:20.)
Moreover, “from among the righteous, [the Lord] organized his forces and appointed messengers, clothed with power and authority, and commissioned them to go forth and carry the light of the gospel to them that were in darkness. …
“And all other principles of the gospel that were necessary for them to know in order to qualify themselves that they might be judged according to men in the flesh, but live according to God in the spirit.” (Doctrine and Covenants 138:30, 33–34.)
The spirit world is not far away. From the Lord’s point of view, it is all one great program on both sides of the veil. Sometimes the veil between this life and the life beyond becomes very thin. This I know! Our loved ones who have passed on are not far from us.
One Church President asked, “Where is the spirit world?” and then answered his own question: “It is right here. … Do [spirits] go beyond the boundaries of this organized earth? No, they do not. They are brought forth upon this earth, for the express purpose of inhabiting it to all eternity.” He also said, “When the spirits leave their bodies they are in the presence of our Father and God, they are prepared then to see, hear and understand spiritual things. … If the Lord would permit it, and it was His will that it should be done, you could see the spirits that have departed from this world, as plainly as you now see bodies with your natural eyes.” (Brigham Young, in Journal of Discourses, 3:369, 368.)
Yes, indisputably there is life after death. Mortality is a place of temporary duration—and so is the spirit world. As inevitable as death is to mortals, so also is an eventual resurrection to those in the spirit world. 
President Smith also saw the leaders the Savior called to take the gospel to Heavenly Father’s children in the spirit world. He named some of them: Father Adam, Mother Eve, Noah, Abraham, Ezekiel, Elijah, prophets that Latter-day Saints know from the Book of Mormon, and some from the last days, including Joseph Smith, Brigham Young, John Taylor, and Wilford Woodruff. These would be some powerful missionaries to teach the gospel of Jesus Christ.
Many of our deceased ancestors will have received a testimony that the message of the missionaries is true. A person living on earth who receives that testimony could ask missionaries for baptism. But those who are in the spirit world cannot. The ordinances of baptism and the temple ordinances are offered only in this world. Someone in this world must go to a holy temple and accept the covenants on behalf of the person in the spirit world. That is why Mormons are under obligation to find the names of their ancestors and ensure that they are offered what they cannot receive there without help.
To read the entire vision of Joseph F. Smith, click here.
See also: Mormon Beliefs: The Plan of Salvation