[Update at end of post][Plus additional notes made re: Second Nephi V and Mosiah VII and VIII]
While working on the “Parsing Nephi” series, which is an analysis of the chapter structure of the original Book of Mormon manuscripts (scribal and printer), based on Royal Skousen’s work on the Book of Mormon critical text, I was struck by the organization of extended or parallel quotations from the Old and New Testament within the Book of Mormon text.
Nephi quotes two chapters of Isaiah in First Nephi. In Second Nephi, Jacob quotes two chapters of Isaiah (with the first two verses from a third), after which Nephi quotes thirteen more chapters of Isaiah, then later gives an interpretive reading of yet another one. Similarly, when the Savior appears to the Nephites after His resurrection, He gives a sermon that closely parallels the Sermon on the Mount found in Matthew 5-7, then later quotes one chapter out of Isaiah and two chapters out of Malachi.
Critics (and even some supporters) of the Book of Mormon often claim that Joseph Smith simply copied (or read out loud to his scribes) chapters from the King James Version into the Book of Mormon manuscript. However, there is no historical or physical manuscript evidence of that happening (all credible historical evidence is, in fact, to the contrary); beyond that, there are meaningful textual variants from the KJV in most of the chapters quoted.
(As a side note, critics also like to characterize this inclusion as “wholesale copying” of “large sections of the Bible”. In truth, it’s only 25 chapters out of nearly 1,200 chapters in the Bible, and 20 of those chapters are from a single book: Isaiah.)
In the modern (1879 and later) LDS editions of the Book of Mormon, the Book of Mormon chapter divisions always correspond on a one-to-one basis to the King James Version chapter divisions (with the exception of tacking Isaiah 52:1-2 onto the end of Isaiah 51). This admittedly does lend itself to the appearance of direct copying.
However, in the original and printer manuscripts (and the first edition) of the Book of Mormon, it is never the case that any single chapter from the KJV corresponds to a single chapter within the Book of Mormon. Thus we have:
- First Nephi VI: Introductory text, followed by Isaiah 48 & 49
- Second Nephi V: The first part of Jacob’s sermon (which includes a cite from Isaiah 49:23), followed by Isaiah 49:24 through 52:2 (note that this does not even follow the KJV chapter divisions)
- Second Nephi VIII: Nephi’s wrap-up of Jacob’s sermon, followed by Isaiah 2 through 5
- Second Nephi IX: Isaiah 6 through 12
- Second Nephi X: Isaiah 13 and 14
- Second Nephi XI: Nephi’s prophecies of the gathering of Israel at the last days, followed by an interpretive reading of Isaiah 29
- Second Nephi XII: More of Nephi’s prophecies of the last days, with a repeated quotation of Isaiah 11:4-9
- Mosiah VII: King Noah begins his reign; Abinidi preaches before King Noah and his priests — the priests ask a question about Isaiah 52:7-10; Abinidi, in turns, asks them about the Ten Commandments (Exodus 20:1-17; also see Deuteronomy 5:6-14).
- Mosiah VIII: Abinidi continues to preach before King Noah and his priests — after stating how the Law of Moses is a type and shadow of the Messiah, he quotes Isaiah 53, then expounds on the Messiah at length
- Third Nephi V: The Savior appears to the people at Bountiful and begins — after a series of interactions with the people — the Sermon at the Temple, corresponding to Matthew 5 through 6:24
- Third Nephi VI: The Sermon at the Temple continues, corresponding to Matthew 6:25 through Matthew 7
- Third Nephi X: The Savior talks about His efforts to establish His Gospel among the Gentiles at the last day; He quotes Isaiah 54; and then He chides the people for the things they have failed to record in their own scriptures.
- Third Nephi XI: A brief introductory verse (3 Nephi 23:14); Malachi 3 and 4 (with more introductory text appended to the start of Malachi 3); and a follow-up description of the Savior expounding the scriptures (3 Nephi 26:1-5).
In sum, the chapter divisions within the original Book of Mormon manuscripts and the 1830 edition provide no support for simple dictation from the King James Version and, if anything, argue against it.
UPDATE [same day]: I couldn’t believe that I was the first person to make this observation, so I dropped a note to Royal Skousen, asking for prior references. He graciously replied and pointed me to his own article, “Textual Variants in the Isaiah Quotations in the Book of Mormon”, found on pages 369-390 of Isaiah in the Book of Mormon (Perry & Welch, eds., FARMS, 1998). Specifically, his “Third Finding” on pages 378-379 is that “The original Book of Mormon chapter divisions of the Isaiah quotations follow a larger thematic grouping, not the interruptive chapter system found in the King James Bible.” He makes the same general observations and has a table that corresponds to the bullet list above for First and Second Nephi.
 “Isaiah in the Bible and the Book of Mormon”, John A. Tvedtnes, FARMS Review: Volume – 16, Issue – 2 (2004), Pages: 161-72.