This rust and uselessness of the chief part of your wealth will testify against you. It will be a testimony to your moral corruption, to your hard-heartedness toward your neighbors.
Your wealth lay so long in storage because of your greed and miserliness that it even became corrupt. Therefore in this corruption of your treasures there is visible proof of your own moral corruption.
“The rotting of riches,” he says, “the eating of garments by moths, and the rust of silver and gold will testify against you. They will convict you of having given nothing.
Therefore in the last days, that is, at the coming of Christ, your wealth will prove to be like a fire gathered for your destruction” (Theophylact).
“And it will eat your flesh.” After the destruction of wealth, judgment will overtake the rich themselves. The same rust that destroyed their wealth is presented as destroying, or eating, the flesh, more precisely the fleshes, of the rich.
This is a bold and original figurative representation. Again it is not inappropriate, since the eating of flesh by rust is once more presented as a special action of God’s judgment.
“Flesh,” or “fleshes,” a word used in the plural with reference to one person, cf. 4 Kgs 9:36, means generally the bodily composition of man, which is subject to destruction.
Here this word is probably chosen to indicate the well-fed bodies of the rich, who lived in luxury and delighted in fleshly pleasures (v. 5).
This rust will eat the flesh of the rich like fire. The image of fire as an instrument of judgment often occurs in the sacred books (cf. Ps 20:10 LXX; Isa 10:16-17; Isa 30:27 and others).
“You have heaped up treasure for yourselves in the last days.” At the end of the depiction of the nothingness of wealth before the nearness of the coming judgment, this is an expressive indication of the extreme futility of amassing such treasures.
It is an act of an utterly perverse direction of moral life. They gathered and gathered, and behold, days will come when all this will turn into nothing.
For whom, then, and for what was all this gathered (Ps 38:7)? By the last days are meant the days of Christ’s coming, which is further described as drawing near (vv. 7, 8, 9).