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Question: What is the difference between the "curse" and the "mark" of the Lamanites?
Question: What is the difference between the "curse" and the "mark" of the Lamanites?
The curse and the mark are two distinct things
The Bible does indeed use the word curse to describe a punishment to be inflicted as the result of disobedience to God’s commandments. For example, in Deuteronomy we see:
The Lord shall send upon thee cursing, vexation, and rebuke, in all that thou settest thine hand unto for to do, until thou be destroyed, and until thou perish quickly; because of the wickedness of thy doings, whereby thou hast forsaken me. Deuteronomy 28:20
John A. Tvedtnes notes the distinction between the curse and the mark that the Lord set upon the Lamanites. 
Thus the word of God is fulfilled, for these are the words which he said to Nephi: Behold, the Lamanites have I cursed, and I will set a mark on them that they and their seed may be separated from thee and thy seed, from this time henceforth and forever, except they repent of their wickedness and turn to me that I may have mercy upon them. Alma 3:14 (emphasis added)
Referring to the passage above, Tvedtnes notes the distinction between the Lamanites having been cursed and having the mark set upon them. The Book of Mormon, however, sometimes does call the mark a curse, as shown in Alma 3:6-7.
And the skins of the Lamanites were dark, according to the mark which was set upon their fathers, which was a curse upon them because of their transgression and their rebellion against their brethren, who consisted of Nephi, Jacob, and Joseph, and Sam, who were just and holy men. And their brethren sought to destroy them, therefore they were cursed; and the Lord God set a mark upon them, yea, upon Laman and Lemuel, and also the sons of Ishmael, and Ishmaelitish women. Alma 3:6-7 (emphasis added)
Although this passage refers to the mark as the curse, it later makes a distinction between the curse and the mark. These passages also indicate that the curse was applied prior to the mark. 
The curse applied to the Lamanites was that they were cut off from the presence of the Lord
Tvedtnes suggests that curse applied to the Lamanites was that they were cut off from the presence of the Lord. Nephi states:
Wherefore, the word of the Lord was fulfilled which he spake unto me, saying that: Inasmuch as they will not hearken unto thy words they shall be cut off from the presence of the Lord. And behold, they were cut off from his presence. 2 Nephi 5:20
A group of Nephites who joined the Lamanites illustrates. Their skin color was not changed because of their rejection of the Gospel but the curse was applied to them. Hugh Nibley describes the situation of the Amlicites:
Thus we are told (Alma 3:13-14,Alma 2:18) that while the fallen people "set the mark upon themselves," it was none the less God who was marking them: "I will set a mark upon them," etc. So natural and human was the process that it suggested nothing miraculous to the ordinary observer, and "the Amlicites knew not that they were fulfilling the words of God when they began to mark themselves; . . . it was expedient that the curse should fall upon them" (Alma 3:18). Here God places his mark on people as a curse, yet it is an artificial mark which they actually place upon themselves. The mark was not a racial thing but was acquired by "whosoever suffered himself to be led away by the Lamanites" (Alma 3:10). 
The mark may vary from group to group
As shown above, the mark may vary from group to group. The Amlicites marked themselves, and this was taken by the Nephites as a sign of divine "marking."
Many LDS have traditionally assumed that the "mark" was a literal change in racial skin color. There are certainly verses which can be read from this perspective. A key question, however, is whether modern members read the Book of Mormon's ideas through their own society's preoccupations and perspectives. American society was (and, to an extent, continues to be) convulsed over issues regarding race, especially black slavery and its consequences.
As a result, nineteenth- and twentieth-century members may have read as literal passages which were far less literal to the Nephites. Douglas Campbell has completed an exhaustive review of all such references in the Book of Mormon.  He found that there were twenty-eight usages of the word "white" or "whiteness" in the Book of Mormon. He divided them into several categories:
- Clothing: symbols of purity or cleanness
- Fruit (of tree of life): luminosity or holiness
- Stone (clear and white): literally white stones are not clear, they are opaque. Thus, white is again a term for holiness or luminosity
- Hair (black or white): a single mention (based on the KJV Sermon on the Mount) uses the term as an allegory or symbol
- Jesus, his mother Mary, or those made pure by him: exquisite, radiant, awe-inspiring
- Gentiles: all Gentiles, thus not about skin color but beautiful, pure, and righteous
- The saved: pure, holy, without spot
- As a pair of contrasts (black and white, bond and free): sets of opposites
- Nephites: See below
Thus, virtually all other uses of the white/black terminology reflects symbolic or spiritual states, not literal color. It is likely that Nephites would not have had the modern American "preoccupation" with skin color, and so would not be burdened with our tendency to see references about skin to automatically imply race.
Thus, concludes Campbell:
White-skinned Nephites and black-skinned Lamanites are metaphors for cultures, not for skin colour. The church teaches that the descendants of the Lamanites inhabited the Americas when Columbus arrived. But Lamanites are not black-skinned; they are not even red-skinned. As the “skin of blackness” is a metaphor, so too is the white skin of the Nephites. Perhaps 3 Nephi 2:15-16, in which the Lamanites have the curse taken from them, fulfills 2 Nephi 30:6. In these verses the Lamanite has become “white and delightsome” not “pure and delightsome.”
I do not believe the Lord changed their physical skin to white in the twinkling of an eye. These Lamanites...became cultural Nephites.
Many languages have such color labels for non-visual matters. As Steven Pinker of the director of the Center for Cognitive Neuroscience at MIT noted:
It's convention, not color vision, that tells us that a sick Caucasian is green, a cold one blue, and a scared one yellow. 
There are also instances in which skin color does not play a role, when it should—if the skin color change is literal and noticeable
There are also instances in which skin color does not play a role, when it should—if the skin color change is literal and noticeable. This should suggest that the literal skin model may be inadequate, since it makes nonsense of a few textual passages.
For example, Captain Moroni wanted to portray his men as being "Lamanites." He searched among his troops for someone descended from Laman, and found someone. Moroni sent this man with a troop of Nephite soldiers, and he was able to deceive the Lamanites:
Now the Nephites were guarded in the city of Gid; therefore Moroni appointed Laman and caused that a small number of men should go with him. And when it was evening Laman went to the guards who were over the Nephites, and behold, they saw him coming and they hailed him; but he saith unto them: Fear not; behold, I am a Lamanite. Behold, we have escaped from the Nephites, and they sleep; and behold we have taken of their wine and brought with us. Now when the Lamanites heard these words they received him with joy...(Alma 55:7-9.)
If skin color is the issue, then a single Lamanite with a group of Nephites should be easy to spot. But, in this case, it is not. Why, then, the need for a Lamanite at all in Moroni's plan?
A "native" Lamanite was probably needed because there were differences in language or pronunciation between cultural Nephites and Lamanites (compare between Ephraim and others' shibboleth, Judges 12:6). Note that the Book of Mormon says that "when the Lamanites heard these words," they relaxed and accepted the Lamanite decoy with his Nephite troops. What they could see had not changed, and surely if a dark-skinned Lamanite shows up with a white-skinned bunch of Nephites, they would be suspicious no matter what he said. But, if Nephites and Lamanites are indistinguishable on physical grounds if dressed properly, then their sudden reassurance when a native Lamanite speaks is understandable.
This fact was probably obvious to Mormon and Captain Moroni. The text does not spell it out for us (since it was obvious to the writers), but the clues are all there for the careful reader.
This passage is nonsensical if literal skin color is the issue. It makes perfect sense, however, if Nephites and Lamanites are often physically indistinguishable, but have some differences in language which are difficult to "fake" for a non-(cultural)-Lamanite. 
- John A. Tvedtnes, "The Charge of 'Racism' in the Book of Mormon," FARMS Review 15/2 (2003): 183–198. off-site
- Hugh W. Nibley, Lehi in the Desert, the World of the Jaredites, There Were Jaredites, edited by John W. Welch with Darrell L. Matthew and Stephen R. Callister, (Salt Lake City, Utah: Deseret Book Company; Provo, Utah: Foundation for Ancient Research and Mormon Studies, 1988), Chapter 4. (emphasis added)
- Douglas Campbell, "'White' or 'Pure': Five Vignettes," Dialogue: A Journal of Mormon Thought 29 no. 4 (Winter 1996), 119–135. off-site
- Steven Pinker, The Stuff of Thought: Language as a Window into Human Nature (New York: Viking, 2007), 115.
- Brant A. Gardner, Second Witness: Analytical and Contextual Commentary on the Book of Mormon, 6 Vols. (Salt Lake City, UT: Greg Kofford Books, 2007), 4:696–697.