According to John Welch, that the choice of Isaiah selections in the Book of Mormon was deliberate is shown by Jacob's statement in 2 Nephi 6:4:
"I will read you the words of Isaiah. And they are the words which my brother has desired that I should speak unto you."
Not all the chapters of Isaiah are included in the Book of Mormon, and certainly not all are explained. But "the Lord had a purpose in preserving the prophecies of Isaiah in the Book of Mormon, notwithstanding they become a barrier to the casual reader." Perhaps understanding why certain Isaiah passages have been chosen rather than others may prevent the prophecies of the Old Testament prophet Isaiah from looming "as a barrier, like a roadblock or a checkpoint beyond which the casual reader, one with idle curiosity, generally will not go." [John Gee, "Choose the Things That Please Me": On the Selection of the Isaiah Sections in the Book of Mormon," in Isaiah in the Book of Mormon, p. 67]