The 1837 edition omitted the pronoun them, which refers to “the words” at the beginning of the passage. This deletion was not marked by Joseph Smith in the printer’s manuscript. This change could be an error that the 1837 typesetter introduced, especially since it was probably influenced by the preceding clause “I should speak unto you”, which is almost identical to the resulting 1837 clause “I speak unto you”. The 1908 RLDS edition restored the direct object them (in accord with the reading in 𝓟).
This omission also makes a clear difference in meaning. The original text means that Jacob and Nephi have selected a specific text of Isaiah for the people’s benefit. When them is omitted, the text means that Jacob’s speaking to the people is generally for their benefit (which seems like an obvious truism).
Summary: Restore in 2 Nephi 6:4 the reading of the original text, “and I speak them unto you for your sakes”.