# Your gold and your silver have become tarnished

"Your gold and silver will become tarnished" 

# have become tarnished ... their rust

"are ruined ... their ruined condition" 

# their rust will be a witness against you. It

"and when God judges you, your ruined treasures will be like someone who accuses you in court. Their corrosion"

# will consume ... like fire

Here the corrosion is spoken of as if it were a fire that will burn up their owners.

# your flesh

Here "flesh" stands for the physical body. 

# fire

The idea of fire here is meant to lead people to remember that fire often stands for God's punishment that will come on all the wicked. 

# for the last days

"for when God is about to judge you"