This passage originally had a sequence of three which ’s (listed above as 1, 2, and 3). Joseph Smith tried to alleviate, it would seem, this repetition of the same relative pronoun by replacing the third which with that. This emendation has been followed in all subsequent editions (from 1837 on). However, while editing the printer’s manuscript, Joseph apparently changed his mind, and he actually ended up deleting his that. Perhaps he felt it conflicted with the following relative pronoun that (namely, “that his seed should have for the land of their inheritance”). This second change would have clearly simplified the overall relative-pronoun usage in this passage (“which is the land the Lord God hath covenanted with thy father that his seed should have”). Unfortunately, Joseph’s crossout of the that is not all that clear (yet there is no doubt that he did cross it out). The 1837 typesetter did not see Joseph Smith’s crossout and so printed the that, which has been followed by all subsequent editions. Thus the current text has two which ’s, followed by two that ’s.
This editing by Joseph Smith is, of course, stylistic. Yet in many instances, he left numerous occurrences of the relative pronoun which in close proximity to each other. See, for instance, the previous verse (1 Nephi 13:29), which has six occurrences of which.
Summary: Restore the one case of which in 1 Nephi 13:30 that was edited to that; the frequent repetition of the relative pronoun which occurs throughout the Book of Mormon text.