When iron is exposed to oxygen and moisture, the oxygen combines with the metal forming a new compound called iron oxide, more commonly known as rust. Metal is consumed when it becomes rusty.
In a similar fashion negativity eats away on us. Exposed to darkness for longer periods of time robs us of our joy. Things are blown out of proportion and we get discouraged. A bad situation always looks worse at night. Under the influence of darkness we are driven to make decisions we later regret. When God created light He overpowered the darkness – we need to remember that. Holding on to the Lord we are able to see in the dark. He has a way for us.
Jesus asks us: Where do we put our heart? Where do we invest our time and resources? In other words: What do we treasure?
God treasures us, and ideally this goes both ways. If we know the Lord He is our treasure. The treasure trove of His love is not subject to rust; and nobody can steal His love away from us.