"You are the light of the world. A city set on a hill cannot be hidden. Nor do men light a lamp, and put it under the peck-measure, but on the lampstand; and it gives light to all who are in the house." Matthew 5:14-15 NASB
Using two simple illustrations, Jesus teaches His disciples that they must not hide their relationship with Him. A city that sits on top of a hill can be seen from afar. A lamp is not turned on to be covered up but to radiate light into a dark room.