Here we have another example where Joseph Smith edited the text (in this case, in the printer’s manuscript) in order to remove an initial fragment. In the original text, the sentence begins with “thou beholdest that the Gentiles”, followed by a long sequence of relative clauses, but no predicate is ever provided for the original subject (“the Gentiles”). Instead, the original text starts over, so to speak, by referring back to the initial idea of beholding or seeing (“wherefore thou seest that … ”). As already noted under 1 Nephi 11:1, Joseph sometimes removed these examples of wherefore-clauses but not always. In any event, such clauses are perfectly understandable and will be maintained in the critical text.
In this example, the wherefore-clause that Joseph Smith deleted introduces new information (namely, the Lord will not allow the Gentiles to completely destroy the surviving descendants of Nephi). Probably because of this added information, Orson Pratt (in his editing for the 1879 edition) decided to restore the original text here in 1 Nephi 13:30, undoubtedly by reference to the 1830 edition (at the time the only available source for the original text). Subsequent LDS editions have followed Orson Pratt’s restoration, but the RLDS editions have continued to follow Joseph Smith’s shorter text, which he specifically marked in the printer’s manuscript.
Summary: Maintain the original wherefore-clause in 1 Nephi 13:30, with its partial repetitiveness; Joseph Smith’s 1837 editing not only corrected the grammar in this passage, but also removed some of the information found in the original text, which is probably why Orson Pratt restored the original reading in the 1879 LDS edition.