In the original text, there are a few instances in relative clauses where the nonstandard use of the second person singular art appears to be intended. Here in Helaman 7:16 is one example: “of him who art seeking to hurl away your souls”. See the discussion under Alma 10:7 for the evidence that art was the original reading here in Helaman 7:16 and in three other passages. In this particular case, Joseph Smith made the grammatical emendation to is in his editing for the 1837 edition.
Summary: Restore in Helaman 7:16 the original art in the relative clause “who art seeking to hurl away your souls”.