Lay not up for yourselves treasures upon earth - Treasures, or wealth, among the ancients, consisted in clothes or changes of raiment, as well as in gold, silver, gems, wine, lands, and oil. It meant an abundance of “anything” that was held to be conducive to the ornament or comfort of life. As the Orientals delighted much in display, in splendid equipage, and costly garments, their treasures, in fact, consisted much in beautiful and richly-ornamented articles of apparel. See Genesis 45:22, where Joseph gave to his brethren “changes of raiment;” Joshua 7:21, where Achan coveted and secreted “a goodly Babylonian garment.” Compare also Judges 14:12. This fact will account for the use of the word “moth.” When we speak of “wealth,” we think at once of gold, and silver, and lands, and houses. When a Hebrew or an Orientalist spoke of wealth, he thought first of what would make a “display;” and included, as an essential part, splendid articles of dress. The “moth” is a small insect that finds its way to clothes and garments, and destroys them. The “moth” would destroy their apparel, the “rust” their silver and gold; thus all their treasure would waste away. The word rendered “rust” signifies anything which “eats into,” and hence, anything which would consume one’s property, and may have a wider signification than mere rust.
And where thieves break through and steal - The houses in the East were not unfrequently made of clay hardened in the sun, or of loose stones, and hence it was comparatively easy, as it was not uncommon, for thieves to “dig through” the wall, and effect an entrance in that way. See the notes at Job 24:16.