Matthew 6:19–20 (King James Bible)
lay not up for yourselves treasures upon earth
where moth and rust doth corrupt
→ and where thieves break through and steal
but lay up for yourselves treasures in heaven
where neither moth nor rust doth corrupt
and where thieves do not break through nor steal
The repeated where is missing in verse 19 of the Book of Mormon text but is in verse 20:
The strong parallelism between all these clauses suggests that for verse 19 a second where may have been in the original Book of Mormon text. The only difference between the two verses is that one is positive and the other negative. Syntactically, there seems to be no strong reason for why the repeated where should be dropped in the positive verse yet kept in the negative one. But the reading without the where will work, so the critical text will follow the earliest text in verse 19 (which lacks the where). The possibility remains that Oliver Cowdery, the presumed scribe here in 𝓞, dropped the where as he was taking down Joseph Smith’s dictation (or Joseph omitted it in his dictation). The original manuscript probably didn’t have this where since both the 1830 edition and the printer’s manuscript lack it.
Summary: Since the earliest reading in 3 Nephi 13:19 without the repeated where will work, the critical text will maintain this reading; however, the strong parallelism between verses 19 and 20, plus the full parallelism in the corresponding Matthew passage, suggests that there may be a primitive error here in verse 19.