John Calvin Commentary James 5:3

"Your gold and your silver are rusted; and their rust shall be for a testimony against you, and shall eat your flesh as fire. Ye have laid up your treasure in the last days." — James 5:3 (ASV)

A witness against you. He confirms the explanation I have already given. For God has not appointed gold for rust, nor garments for moths; but, on the contrary, He has designed them as aids and helps to human life. Therefore, even spending without benefit is a witness of inhumanity. The rusting of gold and silver will be, as it were, the occasion of inflaming the wrath of God, so that it will, like fire, consume them.

Ye have heaped treasure together: These words may also admit of two explanations: — that the rich, as if they would live forever, are never satisfied, but weary themselves in heaping together what might be sufficient until the end of the world, — or, that they heap together the wrath and curse of God for the last day; and this second view I embrace.