Consider this: if there were only one color, let us say blue, and the entire world and everything in it were blue, then there would be no blue. There needs to be something that is not blue so that blue can be recognized; otherwise, it would not “stand out,” would not exist.
In the same way, does it not require something that is not fleeting and impermanent for the fleetingness of all things to be recognized? In other words: if everything, including yourself, were impermanent, would you even know it? Does the fact that you are aware of and can witness the short-lived nature of all forms, including your own, not mean that there is something in you that is not subject to decay?
When you are twenty, you are aware of your body as strong and vigorous; sixty years later, you are aware of your body as weakened and old. Your thinking too may have changed from when you were twenty, but the awareness that knows that your body is young or old or that your thinking has changed has undergone no change. That awareness is the eternal in you – consciousness itself. It is the formless One Life. Can you lose It? No, because you are It.
Eckhart Tolle, Stillness Speaks