You are like salt for everyone on earth. But if salt no longer tastes like salt, how can it make food salty? All it is good for is to be thrown out and walked on.
You are like light for the whole world. A city built on top of a hill cannot be hidden, and no one would light a lamp and put it under a clay pot. A lamp is placed on a lampstand, where it can give light to everyone in the house. Make your light shine, so that others will see the good that you do and will praise your Father in heaven. (Matthew 5:13-16)