Ye are the light of the world. A city that is set on an hill cannot be hid.
Note 9 at Mt 5:14: Light enables us to see. The world, which is in darkness, has to have Christians to release the light of the glorious Gospel of Jesus Christ so that their blinded eyes may be opened (2Co 4:4). Jesus was the light of the world (Isa 49:6; Mt 4:16; Lu 2:32; Joh 1:4-9, 8:12, 9:5, and 12:35-36). His disciples are also called the light of the world (Mt 5:14, Eph 5:8, Php 2:15, and 1Th 5:5). Joh 9:5 shows that as long as Jesus was in the world in His physical body, He was lighting the way to the Father. He now shines through our lives. Again, our responsibility to be witnesses to the world is being stressed. The purpose of a light is to dispel the darkness and allow us to see. Therefore, "let your light so shine before men" (Mt 5:16).