Salt and light

Jesus said to his disciples: ‘You are the salt of the earth. But if salt becomes tasteless, what can make it salty again? It is good for nothing, and can only be thrown out to be trampled underfoot by men.
 ‘You are the light of the world. A city built on a hill-top cannot be hidden. No one lights a lamp to put it under a tub; they put it on the lamp-stand where it shines for everyone in the house. In the same way your light must shine in the sight of men, so that, seeing your good works, they may give the praise to your Father in heaven.’ (Matthew 5:13-16)