A city on a hill cannot be hidden. Neither do people light a lamp and put it under a bowl. Instead they put it on its stand, and it gives light to everyone in the house. In the same way, let your light shine before men, that they may see your good deeds and praise your Father in heaven.
Light is something always noticed in darkness.
Even dim light is noticed. When light is present it enables one to function in what otherwise is darkness. We are light in this world because of faith in Jesus as our Savior. The world naturally is opposed to God. As such, it is in the darkness of its sin and face the eternal consequence of that sin.