Light is used to symbolise God, faith or holiness throughout scripture.
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 others, that they may see your good deeds and glorify your Father in heaven.
Matthew 5:15-16 (NIV)
You wouldn’t turn a light on in your house and then cover it with a thick blanket to stop the light from shining throughout the room. Therefore, when we know just how much God loves us, we shouldn’t hide that away either. Instead we should be sharing that knowledge with those around us. i.e. We need to shine God’s light in this dark world.