I hate rust. Rust means that something once strong will corrode until it is eventually consumed and destroyed. There is a parallel between a corroding metal and sin in the hearts of men. The most valuable metals – gold, platinum, silver, palladium, and rhodium do not corrode. They are noble metals. When I proposed to my wife, I gave her a platinum ring holding a diamond. I wanted it to communicate purity and permanence. Noble metals are not chemically reactive and are not given to rusting the way iron is. Iron will interact with air and water to corrode, especially when salt is present. Cars in the Midwest often rust because the roads are salted to reduce the freezing point in order to prevent ice from forming. Salt is an impurity that changes a property of water and hastens the chemical process of corrosion.
In technical terms, rust is hydrated iron oxide, or iron oxide with water molecules attached to it: Fe2O3·H2O. Water loves to dissolve things – like salt. When salt is dissolved, you get sodium (Na) ions and chloride (Cl) ions which help deliver electrons from iron to the oxygen more rapidly. The full process of rust formation is a tad bit more complicated but suffice it to say that water, oxygen and salt make quick work of anything with iron in it. You can protect the iron by coating it with zinc in a process called galvanization. Better yet, build with a noble metal.
Sin will corrode our hearts and destroy us. We are sinners by nature, like the iron, just waiting to be corroded by elements that surround us – too much temptation, greed, anger, or lust. When we are converted by grace through faith, we are galvanized with a new nature that desires to please God. The old nature remains but now cannot be destroyed thanks to our covering. When we are glorified in heaven, we will finally get to be a noble metal.