The language here is almost identical to the language found two verses earlier:
Yet here in verse 34 Joseph Smith edited the original hath to has rather than the grammatically standard form have. The RLDS text has kept the singular has, which incorrectly implies that the antecedent for the relative pronoun which is “the gospel of the Lamb” rather than “the most plain and precious parts”. Beginning with the 1852 LDS edition, the LDS text has had the grammatically correct have. The critical text will restore the original hath. See the discussion under 1 Nephi 13:32 as well as the general discussion under inflectional endings and subject-verb agreement in volume 3.
Summary: Restore the original hath in 1 Nephi 13:34, just as in 1 Nephi 13:32.