2 Nephi 6-8 
One thing that makes the “Isaiah chapters” of the Book of Mormon difficult is that is that the three major blocks of text are all read into the official record by different narrators at different times for different reasons. They cannot, therefore, be adequately characterized as a single thing. The first group (discussed here), supports Nephi’s argument (and Joseph Smith’s too) that the Lehites are the saving remnant of ancient prophecy–Israelites who will survive the Babylonian captivity and re-establish Zion on the American continent. To argue that a prophecy is being fulfilled, one must cite the prophecy and explain its fulfillment, which is precisely what Nephi does in the first set of Isaiah chapters.
The second set has a very different rhetorical context. It is Jacob, not Nephi, who reads Isaiah 50-51 into the text. And he does so immediately after telling his people that he has seen a vision of the fall of Jerusalem. “For behold, the Lord hath shewn me that they which were at Jerusalem, from whence we came, have been slain and carried away captive,” he affirms; “nevertheless, the Lord hath shewn unto me that they should return again.” (6:8).
Jacob’s desire to mention of the prospect of a return immediately after acknowledging the destruction gives us a sense of how difficult this news must have been for his people. They knew that Jerusalem was going to be destroyed—it’s why they left town after all—but the fact of its destruction must still have affected the Nephites who left the same way that it affected the Jews who survived: it almost destroyed their sense of religious identity, their concept of God, and their understanding of themselves as a chosen people made holy by God’s covenant with Abraham.
It is no accident, then, that the verses that Jacob reads from Isaiah were originally spoken to comfort the Jews who had been carried into captivity–and to assure them that their relationship with God was still intact:
For thus saith the Lord: Where is the bill of your mother’s divorcement? To whom have I put thee away, or to which of my creditors have I sold you? Yea, to whom have I sold you? Behold, for your iniquities have ye sold yourselves, and for your transgressions is your mother put away; wherefore, when I come, there was no man; when I called, yea, there was none to answer. (2 Ne. 7:1-2)
These questions are rhetorical, of course (and more than a little sarcastic, but that’s Isaiah for you). The answer is that God has not divorced Israel, sold them, or put them away. They are the ones who broke up with Him. He remains their God, even though he has allowed Jerusalem to fall. And he invites the people of Israel back to the fold even as they are marching off to their captivity. God reminds them of their covenant and assures them that he has not forgotten:
Look unto Abraham, your father; and unto Sarah, she that bare you: for I called him alone, and blessed him. For the Lord shall comfort Zion: he will comfort all her waste plaees [places]; and he will make her wilderness like Eden, and her desert like the garden of the Lord. Joy and gladness shall be found therein, thanksgiving and the voice of melody. Hearken unto me, my people; and give ear unto me, O my nation: for a law shall proceed from me, and I will make my judgment to rest for a light thing of the people. My righteousness is near; my salvation is gone forth, and mine arm shall judge the people. The isles shall wait upon me, and on mine arm shall they trust. Lift up your eyes to the heavens, and look upon the earth beneath: for the heavens shall vanish away like smoke, and the earth shall wax old like a garment; and they that dwell therein, shall die in like manner. But my salvation shall be forever; and my righteousness shall not be abolished. (2 Ne. 8: 2-6)
Here, in one of the most optimistic passages in all of Isaiah, the prophet invites the Jews to re-establish the Abrahamic Covenant in their captivity—assuring them that, if they turn back to Him, he will remember them and pave the way for their return. This was an important message for the Jews after the destruction of Jerusalem, whether they were captive in Babylon or somewhere in Latin America building pyramids. It was the most important message in the world for the audience that Jacob was trying to reach.
When placed into the actual context of reception, these Isaiah chapters are neither daunting nor difficult: Jacob uses Isaiah to comfort the members of his family after he announces the destruction of Jerusalem. For them, as for the Jews who remained, Jerusalem was an ancestral homeland that conveyed a unique religious identity. Their religion was almost unthinkable without the Temple and the city that surrounded it. Jacob read these words for exactly the same reason that Isaiah first spoke them: to ensure a distraught people that God was still willing and able to redeem them.
But of course it’s not quite so simple. These Isaiah chapters have long been seen by Mormonism’s detractors as strong evidence for 19th century authorship, as they come from a writer (or, more likely, a group of writers) that scholars now identify as “Deutero-Isaiah,” or Second Isaiah (Chapters 40-55). Unlike the original Isaiah corpus (Chapters 1-39), which suggest an 8th century origin, the Deutero-Isaiah chapters all presume that the destruction of Jerusalem has already happened–and they speak directly to the survivors as survivors. It doesn’t take long with a timeline to figure out that anything written after the destruction of Jerusalem could not have been on the Brass Plates of Laban, which Nephi and his brothers seized BEFORE the destruction of Jerusalem. This, in a nutshell, is the Deutero-Isaiah problem in the Book of Mormon.
To avoid grappling with this problem, many Latter-day Saints resist even exploring the view–now generally accepted by scholars in at least some form–that the Book of Isaiah has multiple authors and consists of texts written in both the 8th century, when the Assyrians were threatening the Kingdom of Israel, and in the 6th century, after the Babylonians destroyed Jerusalem. This is, they say, simply the result of secular scholars who don’t believe that an 8th century prophet could have foreseen and reacted to events a century and a half in the future
In his book, Understanding the Book of Mormon, Grant Hardy faces this issue head on, critiquing the positions of Latter-day Saints who dismiss the Deutero-Isaiah problem as “simply the work of academics who do not believe in prophecy.” He asserts that this is “clearly an inadequate (and inaccurate) response to a significant body of detailed historical and literary analysis”  I could not agree more. But I also agree with what Hardy says next: that a more promising avenue for faithful Latter-day Saints “is to acknowledge that we probably know less about what constitutes an ‘inspired translation’ than we do about Ancient Israel. Once one accepts the possibility of divine intervention, the theology can accommodate the (always tentative) results of scholarship.” 
The Deutero-Isaiah chapters in 1st and 2nd Nephi are an uncomfortable presence, but not an inexplicable one, for, as Hardy affirms, accepting a divine provenance for the Book of Mormon provides the theological basis to resolve difficult historical issues. And we do not have a very good sense of what it means for a prophet to translate sacred texts solely through inspiration–with no training in, or knowledge of, the original language.
And once we get past the discomfort of seeing something where we don’t think it should be, we can appreciate the value of Isaiah’s core message in these chapters–a message as comforting to us today as it was to the people of Jacob (and, indeed, the people of Israel): Even at the very moment that we are suffer the natural consequences of our worst decisions and actions, God loves us as a devoted parent and waits patiently, with open arms, to welcome us back into His Kingdom.
 Return readers will remember that, in previous posts, I have tried to cite both the 1830 edition and the modern editions, which divide text into chapters differently. I am officially giving up. I will still read and quote from the 1830 edition, but the citations will all be from modern chapters and verses.
 The three blocks of Isaiah chapters that I refer to are: 1) Isaiah 48-49 in 1 Nephi 20-21; Isaiah 50-52:1-2 in 2 Nephi 7-8; and the very long block of Isaiah 2-14 in 2 Nephi 12-24. A fourth block of a single chapter (Isaiah 29) appears in 2 Nephi 27.
 Hardy, Grant. Understanding the Book of Mormon: A Reader’s Guide. Oxford: Oxford University Press, 2010. p. 69.