And beside all this, between us and you there is a great gulf (χάσμα – Chasma, gaping opening, or impassable interval) fixed: so that they which would pass from hence to you cannot; neither can they pass to us, that would come from thence. (Luke 16:26)
Joseph Fielding Smith said:
We hear the objection made, from time to time, that Jesus did not come to save the dead, for he most emphatically declared himself that there was an impassable gulf that separated the righteous spirits from the wicked. In defense of their position they quote the words in Luke: “And beside all this, between us and you there is a great gulf fixed: so that they which would pass from hence to you cannot; neither can they pass to us, that would come from thence.”
These words, according to the story, were spoken by Abraham’s spirit to the rich man who raised his eyes and asked that Lazarus might go touch his lips and relieve his torment. Abraham replied that it could not be for there was a gulf fixed between them that the spirit of no man could pass. Therefore, say the objectors to the doctrine of universal salvation, “It is quite evident that the righteous and the wicked who are dead cannot visit each other, hence there is no salvation for the dead.”
This was true before the days that Jesus atoned for sin, which is plainly shown in the passage from the Book of Moses previously quoted. And it was at this period this event occurred. However, Christ came and through his death bridged that gulf, proclaimed liberty to the captives, and the opening of this prison door to those who sat in darkness and captivity.
From that time forth this gulf is bridged so that the captives, after they have paid the full penalty of their misdeeds, satisfied justice, and have accepted the gospel of Christ, having the ordinances attended to in their behalf by their living relatives or friends, receive the passport that entitles them to cross the gulf. (Doctrines of Salvation, 2:158)
Paradise is not heaven, or the place where God dwells, but a place of departed spirits. Why the belief should be so general that the thief went to heaven with the Savior is rather strange, since Jesus did not go there until after his resurrection. This fact he disclosed to Mary at the tomb. From the time his spirit left his body until he arose from the tomb, Jesus was with the thief in paradise, according to his promise. There the Savior opened the door for the salvation of the dead. Before that time the unworthy dead were shut up in prison and were not visited. (Moses 7:38-39; Isaiah 24:22.) We have good reason to believe that the righteous spirits in paradise did not mingle with the unrighteous spirits before the visit of our Lord to the spirit world. He declared that there was a gulf fixed that could not be crossed which separated the righteous from the unrighteous, therefore there was no sound of the voice of prophets and the Gospel was not declared among the wicked until Christ went into that world before his resurrection. He it was who opened the prison doors. (Isaiah 42:6-7; 61:1).
President Brigham Young declared that “Jesus was the first man that ever went to preach to the spirits in prison, holding the keys of the Gospel of salvation to them. Those keys were delivered to him in the day and hour that he went into the spirit world, and with them he opened the door of salvation to the spirits in prison.” (Journal of Discourses 4:285.) This is in full accord with the scriptures. President Joseph F. Smith, in the vision he beheld of the spirit world, confirmed this view [see D&C 138]. In that world Christ taught the righteous spirits and commissioned them to carry his message and sent them forth among the unbaptized dead. In this way he fulfilled his promise made to Isaiah that he would preach to the spirits of the dead and open their prison doors that they might go free. (The Way to Perfection, p.315-316)
Bruce R. McConkie wrote:
The spirit prison is hell, that portion of the spirit world where the wicked dwell. (Moses 7:37-39.) Before Christ bridged the gulf between paradise and hell – so that the righteous could mingle with the wicked and preach them the gospel – the wicked in hell were confined to locations which precluded them from contact with the righteous in paradise. Abraham told the rich man in hell that between him and Lazarus (who was in paradise) there was a great gulf fixed so that none could go from paradise to hell or from hell to paradise. (Luke 16:19-31.) Now that the righteous spirits in paradise have been commissioned to carry the message of salvation to the wicked spirits in hell, there is a certain amount of mingling together of the good and bad spirits. Repentance opens the prison doors to the spirits in hell; it enables those bound with the chains of hell to free themselves from darkness, unbelief, ignorance, and sin. As rapidly as they can overcome these obstacles–gain light, believe truth, acquire intelligence, cast off sin, and break the chains of hell–they can leave the hell that imprisons them and dwell with the righteous in the peace of paradise. (Mormon Doctrine, p.755)
By spirit world is meant the abiding place of disembodied spirits, those who have passed from pre-existence to mortality and have also gone on from this temporal world to another sphere to await the day of their resurrection, final redemption, and judgment. This world is divided into two parts: paradise which is the abode of the righteous, and hell which is the abode of the wicked. (Alma 40:11-14.)
Until the death of Christ these two spirit abodes were separated by a great gulf, with the intermingling of their respective inhabitants strictly forbidden. (Luke 16:19-31.) After our Lord bridged the gulf between the two (1 Pet. 3:18-21; Moses 7:37-39), the affairs of his kingdom in the spirit world were so arranged that righteous spirits began teaching the gospel to wicked ones. (Gospel Doctrine, 5th ed., pp. 473-476.)
Thus, although there are two spheres within the one spirit world, there is now some intermingling of the righteous and the wicked who inhabit those spheres; and when the wicked spirits repent, they leave their prison-hell and join the righteous in paradise. Hence, we find Joseph Smith saying: “Hades, sheol, paradise, spirits in prison, are all one: it is a world of spirits. The righteous and the wicked all go to the same world of spirits until the resurrection.” (Teachings of the Prophet Joseph Smith, p. 310.) (Mormon Doctrine, p. 762)