There is something so intrinsic to the identity of what something is, that if it is lost, it can no longer be that which it was created to be. In Matthew 5:13-16, believers are described as the salt of the earth and the light of the world. Jesus emphasizes that just as salt must retain its flavor to be useful and light must shine to illuminate, believers must live out their faith visibly and effectively.

"You are the salt of the earth. But if the salt loses its saltiness, how can it be made salty again? ... You are the light of the world. A town built on a hill cannot be hidden. ... let your light shine before others, that they may see your good deeds and glorify your Father in heaven." (Matthew 5:13-16)