From the Gospel according to Matthew
MT 5:13-16

Jesus said to his disciples: “You are the salt of the earth.  But if salt loses its taste, with what can it be seasoned?  It is no longer good for anything but to be thrown out and trampled underfoot.  You are the light of the world.  A city set on a mountain cannot be hidden.  Nor do they light a lamp and then put it under a bushel basket;  it is set on a lampstand,  where it gives light to all in the house.  Just so, your light must shine before others, that they may see your good deeds and glorify your heavenly Father.”