From The Manifesto (Matthew Chapters 4-7)
The first parabolic illustration used by Jesus is found earlier in Matthew Chapter 4 when He spoke of his disciples as fishers of men. We will consider that illustration at a later time when it is more particularly applied (The Drag-net in Matthew 13:47-50).
A manifesto is a public declaration of policy and aims. The Manifesto delivered by Jesus in the Sermon on the Mount in Matthew Chapters 4-7 revealed laws for the Kingdom of God established upon earth. It includes the beatitudes (“blessed are”). The nature of the kingdom of God is a major theme of Jesus’ teaching and has long been debated by interpreters and scholars, with discussion primarily centering around the nature of the kingdom (earthly, heavenly, or both) and the kingdom’s arrival (present, future, or both). We conclude that at a minimum the manifesto applies to the earthly kingdom at this present time since people on the New Earth will not experience mourning, persecution, or hunger. An additional major issue concerns the relationship between the kingdom of God and the person and work of Jesus himself. They are necessarily and inexorably linked as it becomes impossible to live by these laws without spiritual renewal. The following parables are delivered in this context and to His own disciples.
Salt and Light – Chapter 5:13-16 (NET)
13 “You are the salt of the earth. But if salt loses its flavor,[*] how can it be made salty again? It is no longer good for anything except to be thrown out and trampled on by people! 14 You are the light of the world. A city located on a hill cannot be hidden. 15 People do not light a lamp and put it under a basket but on a lampstand, and it gives light to all in the house. 16 In the same way, let your light shine before people, so that they can see your good deeds and give honor to your Father in heaven.

What subject is our Lord illustrating with salt and light? Jesus had just completed the beatitudes enunciating certain laws of the Kingdom emphasizing that character is supreme, not because of its personal value as much as its influence. This influence is salt and light. Salt arrests corruption and light dispels darkness. Salt works internally; light operates externally irradiating all it reaches.
Salt is aseptic but not antiseptic – it does not cure infection but rather may prevent the spread of infection. If meat is tainted, salt will not make it untainted and pure. The function of the subjects of His Kingdom is to live in the middle of humanity in the terrible condition of sin and by living there according to the ethic of the Kingdom of God, to prevent the spread of evil. It is the Lord’s work to ultimately cure and restore to relationship the cursed, corrupt, and impure spiritual and physical beings. No matter how corrupt or impure God can cleanse it and make it pure.
The subjects of His Kingdom so live that they give goodness, truth, and beauty its opportunity and reduce the spread of sin’s corruptive forces. For discussion we considered the concept of herd immunity i.e. how much salt is necessary to prevent the spread of corruption? Corruption relates to man no longer imaging God. How does mankind image God? By searching for God, having faith in God to supply all of its needs, and prioritizing relationship with God.
In Genesis 6 the daughters of men refer to the offspring of those whose concentration was away from God and on humankind instead. Sons of God were those whose focus was on God. These groups began to intermarry. As a result the focus on God would inevitably wane as the attraction to human care and concern seeped in. And the passage concludes that fact as God describes the whole of humankind as being corrupt (6:3). God then says he will judge “mankind whom I created.” Without any humans seeking God there was no reduction in the spread of sin’s corruptive forces. Humans become mightily corrupted. God cleansed the earth of sin with a worldwide flood.
What does it mean in Matthew 5:13 about salt losing its savor, flavor, or tang? Salt that loses its flavor cannot be salt because it would require a change in its chemical composition. Genuine salt can never lose it flavor. Believers cannot lose their relationship with God.
*This footnote from the New English Translation (NET) Matthew 5:13 The difficulty of this saying is understanding how salt could lose its flavor since its chemical properties cannot change. It is thus often assumed that Jesus was referring to chemically impure salt, perhaps a natural salt which, when exposed to weather, had all the genuine salt leached out, leaving only the sediment or impurities behind. Others have suggested that the background of the saying is the use of salt blocks by Arab bakers to line the floor of their ovens; under the intense heat these blocks would eventually crystallize and undergo a change in chemical composition, finally being thrown out as unserviceable. A saying in the Talmud (the body of the Jewish civil and ceremonial law) attributed to R. Joshua ben Chananja (ca. A.D. 90), recounts how when he was asked the question “When salt loses its flavor, how can it be made salty again?” is said to have replied, “By salting it with the afterbirth of a mule.” He was then asked, “Then does the mule (being sterile) bear young?” to which he replied: “Can salt lose its flavor?” The point appears to be that both are impossible. The saying, while admittedly late, suggests that culturally the loss of flavor by salt was regarded as an impossibility. Genuine salt can never lose its flavor. In this case the saying by Jesus here may be similar to Matt 19:24, where it is likewise impossible for the camel to go through the eye of a sewing needle.
Light refers to a spiritual revelation that is to radiate from the subjects of His Kingdom. Jesus said He is the Light of the World. When we are yielded to God and obeying Him as subjects of His Kingdom, we become His light for the world. Like the moon reflecting the sun we are luminaries reflecting God’s light. Light enables things to be seen by its shining. The light through the Christian in this world illuminates all the worldly order so that men see the true way. As John the Baptist we function as a lamp burning and shining His light (John 5:35).

Two figures are employed: A city on a hill and a lampstand in a house. The city on a hill is for the illumination of vast distances i.e. the corporate body of believers coming together in fellowship to shine collectively to reach the far expanses of life. In your household or circle of friends, you as an individual (lampstand) would not want to hide the light from others who do not know the way.

Perhaps one more point, the lamp is not the light but what holds the light. A lamp or a candle is a dark body and can give no light until it is lighted. God’s Spirit in us is a light that will burn a hole through any bushel and illuminate what is dark within each of us. Salt cannot lose its savor (God’s spirit within). Hence we are the evidence of His redemptive and transforming power.

The Psalmist writes in Chapter 119:105, “Thy word is a lamp unto my feet, and a light unto my path.” Back in Old Testament days the word was mostly the written word. Since then God’s Word became incarnate in Jesus Christ, and now additionally resides with the believer’s spirit (Holy Spirit).