Isaiah 10:17–18 (King James Bible) and the light of Israel shall be for a fire and his Holy One for a flame and it shall burn and devour his thorns and his briars in one day and shall consume the glory of his forest and of his fruitful field
In this passage, the Book of Mormon text is missing the subject it of the King James text in the clause “and shall burn”. Interestingly, this it is not in italics in the King James Bible, which suggests once more that the Book of Mormon text does not strictly follow the King James Bible’s use of italics to determine whether or not to delete a word like the pronoun it. (As part of the critical text project, my research assistants examined the text for 44 different editions of the King James Bible published in the United States at the beginning of the 1800s. In none of those copies was this particular it ever italicized.) For general discussion regarding the italicized it, see 2 Nephi 15:29; for one other example of a nonitalicized King James it being deleted in the Book of Mormon text, see 2 Nephi 17:11.
This passage in 2 Nephi 20:17–18 also provides one more example of increased parallelism: namely, the modal verb shall before the verb devour. Note also that omitting the it also increases the parallelism by giving three instances of and shall: “and shall burn and shall devour his thorns and his briars in one day and shall consume the glory of his forest”. For further discussion of increased parallelism involving shall, see 2 Nephi 17:14–15.
Summary: Retain in 2 Nephi 20:17 the more parallelistic text of the Book of Mormon with its additional shall and omitted it.