As in the reference to the salt, Jesus is illustrating that you have an influence. Your life makes an impact on the lives of others and when His righteousness is resident in your influence should reflect the light of God for the glory of God.
Here is a powerful illustration from the early days of the Faith:
In the days of the Roman Emperor Nero, there lived and served him a band of soldiers known as the "Emperor’s Wrestlers." Fine, stalwart men they were, picked from the best and the bravest of the land, recruited from the great athletes of the Roman amphitheater.
In the great amphitheater they upheld the arms of the emperor against all challengers. Before each contest they stood before the emperor’s throne. Then through the courts of Rome rang the cry: "We, the wrestlers, wrestling for thee, O Emperor, to win for thee the victory and from thee, the victor’s crown."
When the great Roman army was sent to fight in Gaul, no soldiers were braver or more loyal than this band of wrestlers led by their centurion Vespasian. But news reached Nero that many Roman soldiers had accepted the Christian faith. Therefore, this decree was dispatched to the centurion Vespasian; "If there be any among your soldiers who cling to the faith of the Christian, they must die!"
The decree was received in the dead of winter. The soldiers were camped on the shore of a frozen inland lake. It was with sinking heart that Vespasian, the centurion, read the emperor’s message.
Vespasian called the soldiers together and asked: "Are there any among you who cling to the faith of the Christian? If so, let him step forward!" Forty wrestlers instantly stepped forward two paces, respectfully saluted, and stood at attention. Vespasian paused. He had not expected so many, nor such select ones. "Until sundown I shall await your answer," said Vespasian. Sundown came. Again the question was asked. Again the forty wrestlers stepped forward.
Vespasian pleaded with them long and earnestly without prevailing upon a single man to deny his Lord. Finally he said, "The decree of the emperor must be obeyed, but I am not willing that your comrades should shed your blood. I order you to march out upon the lake of ice, and I shall leave you there to the mercy of the elements."
The forty wrestlers were stripped and then, falling into columns of four, marched toward the center of the lake of ice. As they marched they broke into the chant of the arena: "Forty wrestlers, wrestling for Thee, O Christ, to win for Thee the victory and from Thee, the victor’s crown!" Through the night Vespasian stood by his campfire and watched. As he waited through the long night, there came to him fainter and fainter the wrestlers’ song.
As morning drew near one figure, overcome by exposure, one man crept quietly toward the fire; in the extremity of his suffering he had renounced his Lord. Faintly but clearly from the darkness came the song: "Thirty-nine wrestlers, wrestling for Thee, O Christ, to win for Thee the victory and from Thee, the victor’s crown!"
Vespasian looked at the figure drawing close to the fire. Perhaps he saw eternal light shining there toward the center of the lake. Who can say? But off came his helmet and clothing, and he sprang upon the ice, crying, "Forty wrestlers, wrestling for Thee, O Christ, to win for Thee the victory and from Thee, the victor’s crown!"
Are you on the ice or near the fire?