Joshua Sears summarizes Latter-day Saint approaces to Isaiah authorship and the Book of Mormon.
Joshua Sears, "Deutero-Isaiah in the Book of Mormon," Charles Swift and Nicholas J Frederick, eds, They Shall Grow Together : The Bible in the Book of Mormon. (Provo: Brigham Young University, 2022)
The first approach is to dismiss the alleged anachronism on the premise that the Book of Mormon is true and therefore anything that presumes to contradict it is false. While this approach is laudable for its commitment, it may be inadequate for some Saints. A century ago, Elder Talmage reported that when people asked him if he had "looked into" the claimed anachronism of Deutero-Isaiah in the Book of Mormon, his response was to ask them, "Why trouble yourselves about the matter?" and then bear his testimony of the Book of Mormon. More recently, however, President M. Russell Ballard has declared, "Gone are the days when a student asked an honest question and a teacher responded, 'Don't worry about it! Gone are the days when a student raised a sincere concern and a teacher bore his or her testimony as a response intended to avoid the issue. Not every Latter-day Saint will feel the need to explore historical issues such as Deutero-Isaiah, but President Ballard's counsel reminds us that others are best served when they combine faith with studied reasons for belief (see Doctrine and Covenants 88:118).
One set of studied reasons, therefore, is supplied through the second approach, which undercuts the alleged Book of Mormon anachronism by using biblical evidences to argue that Isaiah did indeed write the entire book of Isaiah. Authors following this path have made several worthwhile arguments, pointing out places where certain academic assumptions (like the impossibility of predictive prophecy) are not shared by people of faith, as well as places where some biblical scholars have made claims that go beyond the evidence. At the same time, Latter-day Saint arguments for Isaiah's unity have largely had the goal of convincing the already convinced. Academic scholars studying Deutero-Isaiah have produced numerous book-length studies making the case for an exilic setting, analyzing the changes in theme and style, demonstrating the use of Late Biblical Hebrew, and exploring the dependency on Jeremiah and other exilic texts, among other issue. The Latter-day Saint counterarguments, however, have largely consisted of book chapters, typically six to eight pages in length, that address these topics either superficially or not at all. I am not suggesting that this approach is without merit or that Latter-day Saint scholars could not advance worthwhile arguments for Isaiah's unity in the future, but at present no one has produced an up-to-date defense of Isaiah's unity that addresses all the issues with the detail and rigor that would be necessary to truly challenge the academic consensus on its own terms.
But is a complete rebuttal of the academic consensus even necessary? So have argued that efforts to engage biblical scholarship on it own terms are doomed to an impasse because Latter-day Saint assumptions about scripture and historical-critical assumptions about scripture are simply too divergent to find common ground on key grounds. Others have cautioned that if Isaiah did not write the whole book, and if there are others ways to account for the Book of Mormon's Isaiah quotations, then arguing for unified authorship may not be productive anyway.
The third approach, then, starts, with the premise that working with academic scholarship is the best way forward, even if we cannot accept all its conclusions. It approaches the Book of Mormon's use of Isaiah with greater nuance, suggesting that the Book of Mormon can only prove that the specific chapters it quotes from would have been on the brass plates. Some Latter-day Saints taking this position have explored how the Deutero-Isaiah chapters may have been authored or edited during the century that passed between Isaiah's death and Nephi's acquisition of the brass plates. If the Deutero-Isaiah material was produced relatively close to the Babylonian crises of the early sixth century, that would allow for many of the scholarly observations while simultaneously allowing that those texts could have made it onto the brass plates in time for Nephi's departure.
The fourth approach explores the new space created by challenging those assumptions. It asks how divine intervention may have interrupted the textual transmission of Isaiah and produced results that we cannot completely explain through historical-critical analysis, faithful or otherwise. If God wanted to have "anachronistic" texts put into the brass plate or the small plates of Nephi, he could have found a way to do it. For example, given that the English translation of the Book of Mormon was clearly designed to interact with the King James Version of the Bible, the Isaiah quotations possibly ended up reading a little differently from how they had read on the plates. The possibility of divine intervention at any stage in the development of either the book of Isiah or the Book of Mormon means that the standard assumptions about which versions of Isaiah should have existed at certain points in history may be entirely unjustified.
BYU professor Joshua Sears explores scholarly arguments surrounding Isaiah authorship and the Book of Mormon, summarizes Latter-day Saint approaches, and suggests that ultimately it is a theological question. He places Latter-day Saint views on Isaiah into four categories: 1. Using the Book of Mormon to dismiss the scholarly dating of Isaiah, 2. Arguing for a singular Isaiah author using Biblical evidence, 3. Working with Isaiah scholarship to find nuanced answers, and 4. Exploring how divine intervention might have affected Isaiah in the Book of Mormon.