In the ancient world clothing symbolized wealth and status and was often used as dowry. Rust implies that the hoarded treasure is a precious metal subject to corrosion. Yet, silver and gold do not rust. Regardless of the exact figure, the meaning is quite clear. Treasures hoarded on earth, whether food, garments or money, are never secure.
Thieves break in.
For where your treasure is, there your heart will be also. In Jewish thought the heart represented a person's very being. Which of the two one chooses determines one's destiny. If your eyes are good, your whole body will be full of light. But if your eyes are bad, your whole body will be full of darkness.