What did it mean when Jesus said that we are the light of the world? What was the meaning of believers being salt in the world? What is behind these teachings of Jesus?
Are You Worth Your Salt?
In Matthew 5:13 Jesus said “You are the salt of the earth; but if the salt loses its flavor, how shall it be seasoned? It is then good for nothing but to be thrown out and trampled underfoot by men.”
In ancient times, people were paid by salt and salt was at one time a currency. Salt was paid to Roman soldiers and those who weren’t “worth their salt” received little but those who were worthy received their full allotment, if however salt loses its saltiness it is worthless (v 13). It’s good for nothing more than “to be thrown out and trampled underfoot by men.” When salt lost its saltiness, it was mixed together with gypsum and used to seal roofs in ancient times. The roofs were like another room that the family often used as a family room or as a porch. The word gypsum means “bitter” and the analogy is that when Christians become bitter, their saltiness is lost and they are not good for much more than repairing a leaky roof and only to be trodden under foot. Salt that is tainted is also used for roads as it absorbs moisture and makes the road that much harder. When Christians become tainted by unrepentant sin they are hardened. These types of believers are despised by all, including none believers, and are going to be “trampled underfoot.” No wonder Paul said that our speech is to be seasoned with salt (Col 4:6).
Salt Essential for Life
Did you know that salt (sodium chloride) is the only element that is found in every single cell in the human body? Without salt, humans would die. Indeed, most every organism known to man needs at least some salt to be able to survive. Jesus understood this and that’s why He said that salt is good (Mk 9:50). As the Creator of life, He knew that salt is essential to human life but why does Jesus say that we are to be the salt of the earth or world? That which Jesus said in Matthew 5:13 and Paul repeats in Colossians 4:6 means that if our speech is salted among believers and the unsaved, then we can have peace with one another and maybe even with non-believers (Mk 9:50). This means that our salt can enhance the flavor of any conversation and edify any serving opportunity in the church or the world. This does not mean that we’re to be pouring spoonful after spoonful of salt down people’s throats. Too much salt ruins the flavor but just enough salt can make things more palatable. You can lead a horse to water, but you can’t make him drink…but you can feed him salty peanuts.
Another thing that salt does is that it preserves foods from spoilage and prevents it from being deadly…only good for feeding the pigs. Salt has been used as a preservative for thousands of years and it still is today. Salt acts as a preservative in more than one way. Salt can preserve the life of others for eternity and will prevent mortal decay if we are lightly salting our speech. This type of salt saves the souls of others from eternal destruction and ruin. Do you see the implications of witnessing to a lost, unsalted (and unsaved) world?
Salt also enhances flavor. I cut back on salt several years ago but it took me 2 to 3 years to get used to foods without added salt. In a similar fashion, it takes time to savor our speech and our witness with salt. It doesn’t happen overnight. I still love it on tomatoes because it enhances their flavor. So too can we be a sweet savor to other’s lives with the sweet, salty speech of the Gospel of Jesus Christ. This salt we present to others, in the Person of Jesus Christ, is the flavor of the One Who is ready to forgive and cleanse them from the putrid effects of sin. Today, the world is in desperate need  of this salt because it is corrupt. Wherever salt touches, it always serves to enhance and compliment whatever it comes into contact with. Is that like us?
Another reason Jesus may have said that we are the salt of the earth is that salt is also a cleanser. Many people use crushed ice and salt to clean coffee pot stains. Salt water is great solution to kills germs. People gargle with warm salt water for medicinal purposes and by doing so, can sometimes eliminate a sore throat. Many medicines that doctors still prescribe contain salt and it’s frequently used as a wound sterilizer because it disinfects. By analogy, we can tell others about the One Who has cleansed us from our fatal sin-sickness because by His wounds we are healed (Isaiah 53:5).
Finally, it is worth reminding ourselves that too much salt is unpalatable and can ruin foods and so my witness can be unsavory to non-believers and leave a bad taste in their mouth if I overdo it. A few times in school someone pranked me by unscrewing the top of the salt shaker and when I wanted to add a touch of salt, all of the salt in the shaker was dumped onto my lunch…essentially rendering it useless. Likewise, too much salt is going to leave a bad taste in people’s mouths. No one likes to be force fed anything and nowhere in the Bible did Jesus ever force Himself on anyone or make someone to listen to Him. The gospel is never good when forced upon people. Jesus’ message of salvation  was always offered freely to anyone who would believe (John 3:16). Salt is good but it must get out of the shaker. That means we are not salt to a lost world unless we get out and make contact with those who need this salt.
The Light of the World
When I buy gifts for my mother-in-law I keep in mind that she loves lighthouses. The truth is that we are all lighthouses to a world that is shrouded in the darkness of a stormy sea of death. In Matthew 5:14-16 Jesus said that “You are the light of the world. A city that is set on a hill cannot be hidden. Nor do they light a lamp and put it under a basket, but on a lampstand, and it gives light to all who are in the house. Let your light so shine before men, that they may see your good works and glorify your Father in heaven.”
Like a lighthouse warns ships coming into the harbor in the darkness of night, we are to warn others by the light given to us by Christ. He is the light of the world (John 8:12). If we follow Him, we will not walk in darkness because He illuminates the darkness and keeps us from running into harmful things. When they used to use candles they never put it under a basket (fire hazard!) or under a table but they displayed it openly so that all could see. That is why we are called to be light. Light exposes the darkness and the evil of those things done in the dark because sinners love the darkness so that their evil deeds won’t be seen by others (John 3:19).
We are called to be a light but this does not mean that we shine it in people’s faces because that hurts the eyes. The reason it does is because someone who has been in the darkness for so long is used to darkness and the light hurts their eyes. It takes time to get used to light after having been in darkness for a long time. Jesus said we are to be the light of the world but He did not say we are to shine the light in people’s faces. Nevertheless, we should be a light to the lost because light shows the pathway to all of those in a darkened world. It doesn’t take much light to light up an entire room. One candle can illuminate a huge, dark cave. We are not the source of the light any more than an un-lit candle can shine on its own. It must first receive the light of fire and so we are not the source of the light. The moon is not its own source of light but only reflects the light of the sun that it receives. So too are believers to reflect the Son’s light to expose the darkness to reveal to those who are still residing in darkness a view of what the Son is like. We are to be a light in this sense of being His light because He is the light of men (John 1).
If you are unsalted, that is you are unsaved, then you will face eternal destruction from which there is no recovery. The source of this salt is for all who come to Christ in faith. Once they repent of their sins, confess them, and place their trust in Christ, they will be saved for eternity. Then they can be salt and light to a dark world that doesn’t know where they are going. To expose the darkness and show the way, we need the light of Christ within us. Once this light of the world is believed upon and received, then we can be a light to a lost, dark, decaying world. We are to be the salt and the light but we are not the source of these. Come to the Source and that Source is Jesus Christ. Come to Him all who would be saved (Rom 10:9-13).
Another article you might want to read- How is Satan disguised as an Angel of light 
New International Version Bible (NIV)
THE HOLY BIBLE, NEW INTERNATIONAL VERSION®, NIV® Copyright © 1973, 1978, 1984, 2011 by Biblica, Inc.™ Used by permission. All rights reserved worldwide