Isaiah 10:15 (King James Bible) shall the ax boast itself against him that heweth therewith or shall the saw magnify itself against him that shaketh it as if the rod should shake itself against them that lift it up or as if the staff should lift up itself as if it were no wood
The King James text adds two parallelistic or ’s to clarify the poetic structure of this passage. Both or ’s are in italics in the King James Bible since there are no or ’s here in the Hebrew text. But the Book of Mormon text has only the second or. One would think that the text should have either both of them or neither, so perhaps the missing first or could be an error in the early transmission of the text. The original manuscript is not extant here.
There are a couple of passages where or was initially dropped in the early transmission of the Book of Mormon text:
In the first passage, when copying from 𝓞 to 𝓟, Oliver Cowdery initially wrote “Ammon Aaron Omner or Himni”, but then almost immediately he corrected it to “Ammon or Aaron or Omner or Himni” (there is no change in the level of ink flow). The original manuscript is extant for part of this passage, and the last two or ’s are extant. Apparently the first or occurred at the end of the line in 𝓞. In the second passage (in Moroni 4:1), the 1830 compositor initially omitted the necessary or between elder and priest, then supplied it later as an in-press change. For a couple of other (more complicated) passages where or seems to have been accidentally omitted in copying from 𝓞 into 𝓟, see Alma 58:18 and Mormon 6:10.
These examples suggest that in 2 Nephi 20:15 the first of the two italicized King James or ’s could have been accidentally omitted. Nonetheless, the Book of Mormon text reads perfectly well the way it is, with only the second or. Note that it is clearly easier to omit the first or than the second one. In the first case, we have two rhetorical yes-no questions (“shall the ax boast itself … shall the saw magnify itself ”). These two questions work without any connecting or. On the other hand, in the second case, by omitting the or, we end up with an awkward sequence of three subordinate clauses, each headed by as if:
as if the rod should shake itself against them that lift it up
as if the staff should lift up itself
as if it were no wood
Thus the second or here in Isaiah 10:15 seems necessary and may have been consciously kept, while the first or was unnecessary and may have been intentionally removed. Since the Book of Mormon reading will work with only the second or, the critical text will maintain the earliest extant reading for 2 Nephi 20:15.
Summary: Maintain the earliest reading for 2 Nephi 20:15, which omits the first or of the King James text but retains the second one.