Here the editors for the 1920 LDS edition replaced the modal should with shall. In modern English, the past-tense should characteristically takes a conditional sense. In order to avoid this interpretation for this sentence, the should was replaced by shall. There are a number of places in the text where future uses of should have been grammatically emended to shall, but others have been retained. For some discussion of cases where the 1830 typesetter made this emendation, see under 3 Nephi 1:8. Also see under 1 Nephi 3:19 for discussion regarding Joseph Smith’s editing out of the conditional modal when it referred to the future. The critical text will restore these original instances of past-tense modals such as should even when they refer to future time.
Summary: Restore in 3 Nephi 28:39 the past-tense modal should, the reading of the earliest textual sources; such uses of past-tense modals to refer to future time were fairly common in the original text of the Book of Mormon.