The Book of Mormon's teachings on hell sometimes sound much harsher than what we understand from modern revelation. From Joseph's Smith's revelations, such as his vision on the three degrees of glory in Section 76 of the Doctrine and Covenants and his revelations pertaining to the salvation of the dead and baptism for the dead, we know that many who die without having accepted Christ or without even having heard of Him will have a fair chance to hear and accept the Gospel. We also know that for almost all the wicked who have lived on this planet, the place or condition we call hell is ultimately only temporary for them, though the concept of hell itself is eternal and language about eternal punishment is ambiguous on purpose to stir men up to repentance, as explained in Section 19 of the Doctrine and Covenants (but yes, those who go to the Telestial Kingdom after suffering for their own sins in hell are eternally cut off from the presence of God and Christ, and do not return to them in the Celestial Kingdom).

It is only the sons of perdition who seem to be cast into hell forever, those who fully know the reality of God and Christ and openly fight against them and consent to the killing of Christ--but even then we don't actually know what their end is, if any, so it may not be fair to assume their suffering is endless. Section 76 tells us that the sons of perdition go "into everlasting punishment, which is eternal punishment" (Doctrine and Covenants 76:44). Here we must note that God's punishment by definition is "eternal punishment" since God is eternal, as explained in Section 19, but that doesn't mean that those who suffer such punishment suffer it forever.  Is that the case here as well? We don't know, for the next verse tell us this about their torment: "the end thereof, neither the place thereof, nor their torment, no man knows" (Doctrine and Covenants 76:45). If we don't know the end, it's possible there is one. We don't know. 

Likewise, the warning against falling into "eternal death" (2 Nephi 2:29) does not mean one will never be resurrected, but that one is cast out from God's presence and will "die as to things pertaining to things of righteousness" (Alma 40:26), things which I suggest relate to the majesties of the Celestial Kingdom that the unpenitent wicked will not experience. 

I raise these points because language in the Book of Mormon seems to reflect the view that there is either eternal heaven or eternal hell. Perhaps the strongest language on this point speaks of "never returning" from that state. For example, King Benjamin in Mosiah 2 said:

23 And now I have spoken the words which the Lord God hath commanded me.

24 And thus saith the Lord: They shall stand as a bright testimony against this people, at the judgment day; whereof they shall be judged, every man according to his works, whether they be good, or whether they be evil.

25 And if they be evil they are consigned to an awful view of their own guilt and abominations, which doth cause them to shrink from the presence of the Lord into a state of misery and endless torment, from whence they can no more return; therefore they have drunk damnation to their own souls.

26 Therefore, they have drunk out of the cup of the wrath of God, which justice could no more deny unto them than it could deny that Adam should fall because of his partaking of the forbidden fruit; therefore, mercy could have claim on them no more forever.

27 And their torment is as a lake of fire and brimstone, whose flames are unquenchable, and whose smoke ascendeth up forever and ever. Thus hath the Lord commanded me. Amen. 

Then in 3 Nephi 27, Christ says something similar. Speaking of those who build up false churches not founded upon His Gospel and in His name, He said:

11 But if it be not built upon my gospel, and is built upon the works of men, or upon the works of the devil, verily I say unto you they have joy in their works for a season, and by and by the end cometh, and they are hewn down and cast into the fire, from whence there is no return. 

 Then speaking of the day of judgment, He said:

16 And it shall come to pass, that whoso repenteth and is baptized in my name shall be filled; and if he endureth to the end, behold, him will I hold guiltless before my Father at that day when I shall stand to judge the world.

17 And he that endureth not unto the end, the same is he that is also hewn down and cast into the fire, from whence they can no more return, because of the justice of the Father. 

So it sounds like those who build up false churches or those who fall away from and reject the Gospel will suffer in hell forever. Isn't that rather harsh? How can that be squared with the Restored Gospel of Jesus Christ?

Please note that these scriptures may be examples of the forceful but ambiguous language Doctrine and Covenants 19 speaks of. In fact, they do not say that the wicked or those who rebel will be in hell forever. They will be cast into the fire/torment/hell, but rather than saying they remain forever, instead these verses declare that they don't return. Return? Return to where? This is a critical issue for understanding the scriptures. The verb return requires a frame of reference. Return to where? If I leave Wisconsin by going to China and never return, that doesn't require that I stay in China forever. I may be in China for a week, then go to Europe or New Zealand for years. 

The Book of Mormon concept of "from whence" one does not "return" has to be considered in light of the earliest use of this language in Father Lehi's farewell speech: 

Awake! and arise from the dust, and hear the words of a trembling parent, whose limbs ye must soon lay down in the cold and silent grave, from whence no traveler can return; a few more days and I go the way of all the earth.  (2 Nephi 1:14)

Lehi is bidding farewell to his family and speaks of going soon to the grave, "from whence no traveler can return." So did Lehi mean that for him there would be no resurrection? That he would be dead forever? If so, why did he then go on to bear witness of Christ and the Resurrection, telling us that Christ would "bring to pass the resurrection of the dead" (2 Nephi 2:8)? But here it is clear what Lehi's frame of reference is: the mortal world. Lehi will die and will never return to be among his family and be part of this mortal life. But he knew that he would rise again and have eternal life. But once he died, he would never return to mortality.

So what is the frame of reference in the other verses speaking of the wicked never returning? Obviously, once the wicked are judged by Christ, they are sent out of His presence and will not return to Him and the Father. The language in Mosiah 3:25 is explicitly in the context of the day of judgment, where Christ is the judge. The frame of reference is the presence of Christ. 3 Nephi 27:11 is implicitly referring to the results that come on the day of judgement and 3 Nephi 27:17 also follows an explicit reference to the Father and the Son and the day of judgement in the previous verse. 

The wicked who are cast out of the presence of Christ do not return to Him, but that does not mean they suffer as if they were sons of perdition. Their pains will be great (thus Christ begs us to repent that we may be spared from the pain our sins can bring in Doctrine and Covenants 19), their regret may endure, but they will not rot in hell forever and will at last obtain a merciful kingdom of glory, though far short of what the Father hoped they would receive.

Like Lehi never returning from the grave, the language about the wicked never returning from hell needs to be followed by the simple question: return to where? With the right frame of reference, and through considering the Lord's intent in motivating us to repent, the Book of Mormon's language may fit the more extensive revelations of the modern Church better than we may have realized. 

Update, Dec. 31, 2020: Mormon 9:13 provides another clear indication about the limits on the words "eternal" and "endless" as Moronu  explains that through the Resurrection of Christ, we will all awake  from the "endless sleep" of death and be freed from the "eternal band of death." I discuss this in a subsequent post.