In Doctrine and Covenants (D&C), The LDS (Mormon) church says about the D&C that,
Though there may be those who consider the Doctrine and Covenants prophecies pertaining to this last day (D&C 45:42; D&C 64:24) before Christ’s coming to the world as mere hyperbole, such is not the case. There is an undeniable literalness to the Doctrine and Covenants. Hence, the admonition to “search these commandments, for they are true and faithful, and the prophecies and promises which are in them shall all be fulfilled.
So then, we are to take the D&C undeniably literally, according to the above citation. This is not only devastating to the Mormon faith, but also to Joseph Smith himself.
In D&C section 45, we find several things that not only take away from the Revelation of Jesus, but that also add to the Revelation of Jesus in the Bible. For instance, in verses 64-66 in D&C, it says,
Wherefore I, the Lord, have said, gather ye out from the eastern lands, assemble ye yourselves together ye elders of my church; go ye forth into the western countries, call upon the inhabitants to repent, and inasmuch as they do repent, build up churches unto me. And with one heart and with one mind, gather up your riches that ye may purchase an inheritance which shall hereafter be appointed unto you. And it shall be called the New Jerusalem, a land of peace, a city of refuge, a place of safety for the saints of the Most High God…
This is a very different description of the New Jerusalem and how we are to be a part of it than what the book of Revelation says:
Then I saw a new heaven and a new earth, for the first heaven and the first earth had passed away, and the sea was no more. And I saw the holy city, New Jerusalem, coming down out of heaven from God, prepared as a bride adorned for her husband. And I heard a loud voice from the throne saying, “Behold, the dwelling place of God is with man. He will dwell with them, and they will be his people, and God himself will be with them as their God…
The Spirit and the Bride say, “Come.” And let the one who hears say, “Come.” And let the one who is thirsty come; let the one who desires take the water of life without price.
One says that the New Jerusalem is purchased through the gathering of riches, and the other says that the New Jerusalem will come down from heaven. The D&C, by saying this, both takes away from the Revelation and adds to it. The reason this is an issue is because in the Revelation, we find the following:
I warn everyone who hears the words of the prophecy of this book: if anyone adds to them, God will add to him the plagues described in this book, and if anyone takes away from the words of the book of this prophecy, God will take away his share in the tree of life and in the holy city, which are described in this book.
The idea here is that the description of the objective reality found within the Revelation is not to be changed in any way. But as we can see, this is exactly what the D&C does.
 This book was produced in modern times, according to the LDS church. This makes the D&C to come chronologically after the Revelation, and without question takes away from and adds to “the words of the prophecy of this book,” speaking of the Revelation itself.
I think this should cause a stir in the mind of the Mormon. How is this issue dealt with theologically speaking? It seems that likely Deuteronomy 4:2 will be considered by the trained Mormon person. It says, “You shall not add to the word that I command you, nor take from it, that you may keep the commandments of the Lord your God that I command you.” Mormons often use this to say that there is more words after this verse, so then basically it doesn’t matter. The problem is that this verse is strictly speaking of commandments. It should be understood as adding or taking away from the commandments. If it were mere words that were the issue in this verse, then the human author himself would be breaking the Law that he just wrote down. So would Joshua, Ruth, Samuel, King David, Matthew, Mark, Luke, John, Paul, etc. The idea that Deuteronomy 4:2 is a strong argument for the permission that Mormons can add to scripture is absurd. In fact, it fails completely. The Revelation passage above speaks of prophecy, the Deuteronomy passage speaks of commandments. These are two different subjects entirely.
Since the Doctrine and Covenants are admittedly written by Joseph Smith as discussed above, it seems safe to believe that he is cursed with the plagues described in the Revelation, and also that God will take away his share in the tree of life and in the holy city which are described in the Revelation. What does this say about the rest of the things that he said and did? What does this tell us about what kind of a man was Joseph Smith?
The Book of Mormon, because it teaches a different gospel than what the Bible teaches, in fact, different than what the Revelation specifically teaches, can be included in the curse from the Revelation. Take for instance Revelation 1:5-6, “To him who loves us and has freed us from our sins by his blood and made us a kingdom, priests to his God and Father, to him be glory and dominion forever and ever. Amen.” This verse is the gospel. The good news that people are freed from sin by the blood of Christ. The gospel (which is really no gospel at all), in the book of Mormon is found in 2 Nephi 25:23, which says, “…for we know that it is by grace that we are saved, after all we can do.” This is saying something very different than what the gospel in the Revelation says. It is through this that we can understand how the Book of Mormon adds to, and takes away from, the Revelation. As far as prophecy is concerned, the entire book of Revelation is prophetic. A prophet is one who speaks the will of God to others. It is in this sense, that a prophet can reveal the future through the power of God, which is most of the content of the Revelation, and a prophet by definition, can reveal the will of God by stating what is already known, such as the gospel in Revelation chapter one. When we read Revelation 22:18-19, we should understand this as meaning the entire book, not just certain parts.
Because the Revelation agrees with the rest of the Bible, especially considering the New Testament, we could also say that the Book of Mormon is an addition to the Bible, which would fall under the same curse, because the New Testament agrees with the Revelation chapter one passage discussed above. Whereas the Book of Mormon does not.
This is devastating to the Mormon faith because it was written by a man who will because of his actions (or has) apparently receive curses from God according to Revelation chapter 22, and because it flat out contradicts what the Bible teaches. It is not the Bible that is corrupted, it is Joseph Smith.
Where else does the D&C or Book of Mormon contradict what the Bible teaches or add to the prophecy of the Revelation? Tell us in the comments!
Written by Nace Howell through the grace of the Lord Jesus
 D&C 45:64-66. https://abn.churchofjesuschrist.org/study/scriptures/dc-testament/dc/45?lang=eng. Emphasis mine.
 Revelation 21:1-3, 17. https://www.biblegateway.com/passage/?search=revelation+21&version=ESV. Emphasis mine.
 The point of the New Jerusalem being a bride is because God will be her Husband and will attend to “her.”
 Revelation 22:18-19. https://www.biblegateway.com/passage/?search=Revelation%2022&version=ESV
 Deuteronomy 4:2. https://www.biblegateway.com/passage/?search=deuteronomy+4&version=ESV
 Revelation 1:5-6. https://www.biblegateway.com/passage/?search=revelation+1&version=ESV
 2 Nephi 25:23. https://abn.churchofjesuschrist.org/study/scriptures/bofm/2-ne/25?lang=eng#:~:text=Chapter%2025.%20Nephi%20glories%20in%20plainness%E2%80%94Isaiah%E2%80%99s%20prophecies%20will,Christ%2C%20who%20is%20the%20Holy%20One%20of%20Israel.