This quote is saying that once a person’s body dies, it eventually becomes part of the earth’s soil or dirt. Everything that we are, everything that made us unique, is nothing but stardust and rust after death. Rust is a reddish-orange color caused by oxidation, which is a chemical reaction that happens when different metals are exposed to oxygen, and stardust is tiny dust particles made up of metals and minerals that come from outer space. After we die, our body breaks down and mixes in with the dirt, which means all that is left is rust and stardust.