The 1837 edition omitted the pronoun whatsoever and the finite verb was. This change is probably due to editing on the part of Joseph Smith, although he did not mark the deletion in the printer’s manuscript. The original reading does seem a little awkward, although there is nothing overtly difficult with that expression. Here the word whatsoever acts like the restrictive relative pronoun that, so that “every means whatsoever was in their power” is equivalent to “every means that was in their power”. The antecedent for whatsoever is every means, a semantic plural that agrees with the plurality inherent in the word whatsoever.
A similar use of whatsoever as a relative pronoun occurs for the overtly plural noun phrase all things, as in these examples elsewhere in the text:
There are also three examples of this phraseology in the Book of Mormon that follow the language of the King James Bible:
The King James Bible has three more instances of this construction, all in the New Testament. But note that all these examples, both in the Book of Mormon and the King James Bible, involve the universal quantifier all rather than the semantically equivalent every. In other words, there are no examples like “every thing whatsoever did belong to them” (the equivalent to 3 Nephi 6:1). Thus the language of “every means whatsoever was in their power” is unique to the Book of Mormon text. In Early Modern English, however, we can find examples of every thing postmodified by a whatsoever-clause; here are some examples from Literature Online , with accidentals regularized:
The last citation is interesting since at the end it also has an instance of “all things whatsoever”, the semantic equivalent to “every thing whatsoever”. The critical text will therefore restore the earliest reading in Helaman 6:20 (“every means whatsoever was in their power”) since that expression is clearly intended and we can find evidence for it in Early Modern English.
Summary: Restore the original whatsoever was in Helaman 6:20, thus “and they did use every means whatsoever was in their power to destroy them off the face of the earth”; this expression is supported by seven instances in the Book of Mormon of all things followed by a whatsoever-clause (plus five instances of the same construction in the King James Bible); the singular “every means whatsoever” is also supported by examples in Early Modern English of the parallel expression “every thing whatsoever”.