“Let your light shine before others, so that they may see your good works and give glory to your Father in heaven.”
For those who trust in Him, Jesus truly is that light within us. The light of the Gospel which Jesus had shared with His apostles was to be declared and shared with the world. Therefore they were to be lights of the world. By being a light to the world their sincerity and integrity shone forth. God is glorified by His lights to the world.