Old World Context: The parallels in verses 19 and 20 establish that a treasure is “laid up,” both of which are attacked by “moth” and “rust.” Earthly treasure is vulnerable to those attacks; heavenly treasure is not. Treasure as a metaphor would be particularly tempting to poor people, although affluent Saints are by no means immune from this temptation. The irony is that these transient earthly treasures would be immediately useful, while permanent heavenly treasure cannot be used for immediate mortal comforts. Like many of the Beatitudes, Jesus teaches that we should look forward to the rewards of heaven rather than the rewards of earth.
Book of Mormon Context: This lesson is particularly important to the Nephites since greed for temporal wealth has traditionally underlain heresies (e.g., the Nehors) and political instability (the Gadiantons). The Nephites in Bountiful had resisted these temptations but certainly would be aware of their dangers.
Comparison: There are no changes from the Matthean text. In both the 3 Nephi and Matthew redactions, this verse begins a set of unrelated teachings. Other sections of the sermon had been linked by thematic threads, but the gospel principles explained in verses 19–34 have no discernible relationship to each other (nor do those found in 3 Nephi 14:1–12).
Translation: The Greek word brosis translated in the King James Version as “rust.” Alan Hugh M’Neile suggests: “Brosis is usually explained as ‘rust’. But brosis never has this meaning; in the LXX [Septuagint] it is always the ‘act of eating,’ or ‘food’. It probably denotes, therefore, the ‘devouring,’ by mice or other vermin, of wealth stored in barns.” A better translation from the Greek might be “moth and worm” rather than “moth and rust.” The implication behind “treasure” is therefore fabric and food rather than metallic wealth. “Rust” would not afflict precious metals in any case, although silver does tarnish. “Moth and worm” would have better fit the New World, which lacked a monetary economy; nevertheless, Joseph left the text as “moth and rust.”