Jesus said that we are "the salt of the earth" and "the light of the world". Being salt and light is not optional. Jesus did not say you can be...or you have the potential to be...He said you are. Everyone who has trusted Christ for salvation and is born again is the salt of the earth and the light of the world.
The value of salt, especially in the ancient world can not be under estimated. Roman soldiers received their wages in salt. The Greeks considered salt to be divine. The Mosaic Law required that all offerings presented by the Israelites contain salt. (Lev. 2:13) When Jesus told his disciples that they were "the salt of the earth", as recorded in Matthew 5:13, they understood the metaphor. While the universal importance of salt is not as readily apparent in our modern world, the mandate that Jesus gave to his first disciples is still relevant and applicable to His followers today.
What are the characteristics of salt that caused the Lord to use it in this context? Theologians have different theories about the meaning of "salt" in Matthew 5:13. Some think that its whiteness represents the purity of the justified believer. Others say that salt's flavoring properties imply that Christians are to add divine flavor to the world. Still others believe that Christians are to sting the world with rebuke and judgment the way salt stings an open wound. Another group asserts that, as salt, Christians are to create a thirst for Christ. Salt, however, has another vital purpose which is probably what the Lord had in mind-it stops decay. When Jesus said, "You are the salt of the earth", He meant that all of His disciples were to serve as preservatives, stopping the moral decay in our sin infected world.
Those first disciples would have been intimately familiar with this function of salt. Without refrigeration, the fish that they caught would quickly spoil and rot unless they were packed in salt. Once salted, the fish could be safely stored and then used when needed. The spiritual health and strength of the Christian is to counteract the corruption that is in the world. Christians, as salt, are to inhibit sin's power to destroy lives. This in turn creates opportunity for the gospel to be proclaimed and received.
We have been given a wonderful privilege to be the salt of the earth, but Jesus gave us a warning. The second half of Matthew 5:13 states: "But if salt loses its taste, how would its saltiness be restored? It is no longer good for anything, except to be thrown out and trodden underfoot by men". Jesus did not say that we can lose our salvation; He said that we can lose our saltiness. When salt is contaminated it becomes corrosive and poisonous. Contaminated salt cannot even be used for fertilizer on the field, so it has to be thrown on the road. If we have allowed disobedience, carelessness and indifference to rule our lives, we have become contaminated salt and have lost our saltiness. We need to confess our sin and let the Lord restore us to the purpose for which we were called.
In Matthew 5:14, Jesus tells His disciples, "You are the light of the world". As "salt", the Christian is to counteract the power of sin. As "light" we are to illuminate or make visible. Our lives are to be an on-going witness to the reality of Christ's presence in our lives. When we worship God with pure hearts, when we love others as ourselves, and when we do good without growing weary, we are lights shining. It is important, however to know that it is not our light, but the reflection of the Light of the world, Jesus Christ Himself, that people will see in us.