As discussed under Mosiah 23:13–14, the original text sometimes allowed a sentence-final presentparticipial clause to be connected by means of an and to a preceding main clause; see under that passage for other examples of this original usage. Here in Helaman 4:21–22, the editors for the 1920 LDS edition omitted the thus and changed the nonfinite seeing to the finite they saw, thereby making the sentence end with a finite clause. Although the original usage is awkward, it is fully intended, and thus the original thus seeing will be restored in the critical text.
It should be noted that the deletion of the narrative connector thus was unnecessary. The change was marked in the 1920 committee copy, so the deletion of the thus was not a typo. Perhaps the 1920 editors felt that the ideas in verse 22 repeated the ideas in the previous verse rather than deriving logically from them; in other words, the thus was not consequential or resultive and therefore seemed unnecessary. Yet thus frequently has a summarizing purpose in the Book of Mormon text, as in the following example:
Summary: Restore the original nonfinite seeing in Helaman 4:22 (“and thus seeing that their laws had become corrupted”); this kind of present-participial construction can be found elsewhere in the original text; the thus in this passage acts as a summarizing narrative connector and will also be restored.