Go to now, ye rich men, weep and howl for your miseries that shall come upon you. Your riches are corrupted, and your garments are motheaten. Your gold and silver is cankered; and the rust of them shall be a witness against you, and shall eat your flesh as it were fire. Ye have heaped treasure together for the last days.
James 5:1-3

God is saying, "Wicked rich man, don't just cry; weep and howl! I have evidence against you. You are guilty of withholding more than is meet."

He continues by saying that the gold and silver they amassed, trusted, and loved so much will turn on them and torment them. It is going to eat their flesh as if it were fire. Their actions will devour them.

If you dropped out of high school and decided that you were going to live on the streets and do things your way, your decision would eventually cause your own poverty. Likewise, James was saying that greedy, rich people who hoard wealth for themselves ensure their own destruction.