Although the Book of Mormon generally agrees with the King James Version (KJV) of the Bible both in its acceptable scriptural idiom of translation and in its direct quotations from Isaiah, Joseph Smith's translation of the Isaiah texts in the Book of Mormon sometimes differs. At 2 Nephi 20:29, for example, Joseph dictated Ramath instead of the usual "Ramah" of the parallel King James Isaiah 10:29. Indeed, there is no "t" in the Hebrew text, the Greek Septuagint, or even in the Syropalestinian Aramaic version. The "t" appears, however, in the later Jewish Aramaic translation known as Targum Pseudo-Jonathan, as well as in the Christian Syriac Peshitta version. The words there are Ramata and Rameta, respectively (as is also evident in the Old Syriac Rametha for New Testament Arimathea in Matthew 27:57). Neither source was available to Joseph.Since Isaiah 29 and 2 Nephi 27 were mentioned above, let me point out that critics sometimes have argued that Nephi's many additions to Isaiah 29 in 2 Nephi 27 (or more broadly, in 2 Nephi 26 and 27) is unscriptural, contrary to Jewish tradition, a case of obvious forgery by Joseph Smith, etc. In reality, it is a good example of a Jewish prophet and teacher of the Jewish scriptures showing how a man of God applies scriptures prophetically, showing us how to "like them unto us." Grant Hardy pointed out that Nephi's complex combination of his own words with those of Isaiah could be viewed as akin to the rabbinical "midrash." No, this is not something that comes from wearing your belt too tight. It's related to the Jewish tradition of providing commentary and interpretation of scripture. Grant Hardy explains in his short essay "2 Nephi 26 and 27 as Midrash" and more fully in his chapter of the magnificent book, Reading Nephi Reading Isaiah: Reading 2 Nephi 26–27, edited by Joseph M. Spencer and Jenny Webb (Salem, Oregon: Salt Press, 2011). Yes, what Nephi does with Isaiah 29 is so interesting and instructive, and so related to Book of Mormon themes and to other parts of the text, that there is an entire book written on this topic with some essays definitely worth pondering. I hope you'll enjoy it and come away with a better feel for who Nephi was and how he approached scripture as a reader, an expositor, and a prophet.
Another difference from the KJV came when Joseph was dictating from Isaiah 48:11 in 1 Nephi 20:11. Among other things, Joseph added an "it" that does not appear in the Greek or Hebrew texts. However, the "it" is in one Syriac manuscript, in one Jewish Aramaic Targum manuscript, and in a scribal correction to the large Isaiah Scroll from Qumran Cave One (the latter being the earliest Hebrew text of Isaiah).
King James "Ariel," a poetic term for Jerusalem, is not to be found in the 2 Nephi 27:3 quotation of Isaiah 29:7. However, it is also absent from the Jewish Aramaic Targum—which replaces it with "the City." The Book of Mormon reads Zion instead. This fits well, however, since "Mount Zion" appears at the end of the verse (Isaiah 29:8), and "Zion" and "Mount Zion" parallel each other here....
At 1 Nephi 7:11, the Original and Printer's Manuscripts of the Book of Mormon, as well as the 1830 edition of the Book of Mormon, all use the word how, which was changed in the 1837 and all subsequent editions to read what. However, even the King James translators could not decide, in translating a closely similar phrase in 1 Samuel 12:24, whether how or what was a more accurate translation of the Hebrew relative particle 'asher. They thus placed the one in the text and the other in the margin (the reasons for marginal readings are explained at length in the introduction to their 1611 edition of the King James Version). Exactly the same variant readings occur in the texts we have of the Title Page of the Book of Mormon.
There is an interesting confusion between things and words at 2 Nephi 6:8 and 33:4. While the Printer's Manuscript reads things at both locations, all editions (except the 1830 at 2 Nephi 33:4) have changed this to read words. Either variant is a good reading, and the Hebrew word debarim is accurately translated either "things" or "words."
The 1981 edition of the Book of Mormon has returned for the first time to the reading of the Printer's Manuscript father (singular) at Jacob 3:5, which of course refers directly to Lehi in the preceding Jacob 2:27, 34. The plural form fathers, which had been mistakenly used in all editions since 1830, suggested that Jacob attributed a restriction on plural marriage to earlier Israelite fathers, whereas historical evidence of any such legal restriction before Lehi is lacking.
These, and many other examples, show the significant and interesting things that textual criticism can teach us about the words of the Book of Mormon.
So who was Nephi, or rather, who wrote the text of First and Second Nephi? I'll offer a view based on my study of his writings: he wasn't a 19th century farmboy, nor a 19th century scholar, nor a 19th century expert in the Bible. He was a prophet of God from a troubled family in ancient Jerusalem where he suffered years of abuse from his brothers and struggled all his life with the anger and frustration this caused. He was a brave man who endured a difficult trek through the Arabian Peninsula where he described directions and locations that make sense 2600 years later. He crossed the ocean and took part in leading and teaching people in an incredible adventure in the New World. Most important of all, he was a prophet of God who communed with angels, had visions, and even saw the future Messiah and stood as a witness for the Savior, Jesus Christ, leaving us his sacred writings and commentary to help being us unto Christ.
Other resources to consider related to 2 Nephi 26-27: