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. The treasure trove of His love is not subject to rust; and nobody can steal His love away from us.