Biblical Truth: Believers impact society for Christ when they help preserve it by their influence, project the light of Christ’s love on it by their good works, and seek to promote godly righteousness within it.
Preserve Influence: Matthew 5:13.
 “You are the salt of the earth; but if the salt has become tasteless, how can it be made salty again? It is no longer good for anything, except to be thrown out and trampled under foot by men.” [NASU]
What did Jesus mean when He said that Christians are salt? The mood of the verb is indicative (a statement of fact), not imperative (a command to be something). Jesus is not urging His disciples to become something they are not; He is telling them what they are as kingdom people. The implication is that they are to be what God has thus made them. Like salt, Christians may seem small and insignificant, powerless in a power-mad society. Yet they have the ability to influence every segment of it and to permeate the whole. Salt is cheap; its value is minimal. But salt has unusual properties that far exceed its value. So it is with the members of God’s kingdom. In Jesus’ day salt was a vital preservative. Christians whose lives exhibit the qualities of the ‘blessed’ will have a preserving impact upon a society that, if left to itself, will rot and deteriorate. Without the influence of the gospel, society will suffer moral decay and become putrid. It is important, if our lives are to make a moral impact on others, that we live as Christians among them and take our stand right from the very start. Jesus’ illustration of salt is an encouraging reminder that the apparently cheap and insignificant can influence its environment out of all proportion to our expectation.
We are familiar with another property of salt: it not only preserves, but it also seasons. One meaning of the word ‘season’ is ‘give zest to.’ Christians should have zest. The presence of God’s people should increase the favor of life in many different ways. Everything about us should express the attractiveness as well as the holiness of our Lord. Jesus Himself had this zest. By His very presence He raised the spirits of people. Jesus’ attractiveness did not draw attention to itself. It did not need to, because it was genuine. You do not need to draw attention to real quality, it speaks for itself. Paul tells us that our speech in particular should be seasoned with salt [Col. 4:6]. He explains what he means in the parallel passage [Eph. 4:29]: Let no unwholesome word proceed from your mouth, but only such a word as is good for edification according to the need of the moment, so that it will give grace to those who hear. Interestingly, it is in this context that Paul urges us not to grieve the Holy Spirit. Why in this context? Because our speech is one of the best measurements of the condition of our spirit. Speech is like salt: too little, and we do not taste the flavor of the food; too much, and we are left with the unpleasant taste of the salt. Like salt, our lives and our speech are to bring out the flavor of Jesus Christ.
One further use of salt in Jesus’ culture may have been in His mind as He used this illustration. Sacrifices were accompanied with salt, described as ‘the salt of the covenant of your God’ [Lev. 2:13]. This salt of the covenant was a symbol of faithfulness. In the last analysis, this is what makes the Christian different! He is faithful, both to his Lord and to others. Jesus emphasizes that our ability to preserve the world in order that it may see Christ in us depends on our being different. Not different in a way that draws attention to ourselves, but different in a way that draws attention to Christ. If we have no moral ‘bite’ in the different quality of our lifestyle, then we are no longer salt in the world. How is this possible? What is it that helps Christians retain their ‘saltiness’? As we open our lives to the impact of the whole of Scripture, with its message of a whole Christ, then the whole of our lives will begin to radiate His saving power and grace (John 17:15-19).
Project Light: Matthew 5:14-16.
 “You are the light of the world. A city set on a hill cannot be hidden;  nor does anyone light a lamp and put it under a basket, but on the lampstand, and it gives light to all who are in the house.  Let your light shine before men in such a way that they may see your good works, and glorify your Father who is in heaven.” [NASU]
What this light is Jesus clarifies as our good works, which is a general expression to cover everything a Christian says and does because he is a Christian, every outward and visible manifestation of his Christian faith. Since light is a common biblical symbol of truth, a Christian’s shining light must surely include his spoken testimony. As the disciples of Jesus, we are not to conceal the truth we know or the truth of what we are. There is a fundamental difference between Christians and non-Christians, between the church and the world. The Sermon is built on the assumption that Christians are different, and it issues a call to us to be different. Probably the greatest tragedy of the church throughout its long and checkered history has been its constant tendency to conform to the prevailing culture instead of developing a Christian counter-culture. We must accept the responsibility which this distinction puts upon us. Salt and light have one thing in common: they give and expend themselves – and thus are the opposite of any and every kind of self-centered religiosity. The function of salt is largely negative: it prevents decay. The function of light is positive: it illumines the darkness. So Jesus calls His disciples to exert a double influence on the secular community, a negative influence by arresting its decay and a positive influence by bringing light into its darkness.
Promote Righteousness: Matthew 5:17-20.
 “Do you think that I came to abolish the Law or the Prophets; I did not come to abolish but to fulfill.  For truly I say to you, until heaven and earth pass away, not the smallest letter or stroke shall pass from the Law until all is accomplished.  Whoever then annuls one of the least of these commandments, and teaches others to do the same, shall be called least in the kingdom of heaven; but whoever keeps and teaches them, he shall be called great in the kingdom of heaven.  For I say to you that unless your righteousness surpasses that of the scribes and Pharisees, you will not enter the kingdom of heaven.” [NASU]
Ignorance of the nature and design of the law is at the bottom of most of our religious mistakes. In these verses Jesus explains to us the place the law should have in the Christian life. What is the law? The meaning of the word law can be determined only by examining its use in each context. What, then, does Jesus mean when He speaks about the law in the course of the Sermon on the Mount? Here He is referring particularly to the idea of the law as the specific commandments God has given to His people to regulate the whole of their lives – moral, religious, social, and political. What He goes on to say in 5:21-48 emphasizes that when He speaks about the place of the law, He is thinking of the commandments God gave to His people through the ministry of Moses. Jesus explains the place the law is to occupy in the
(1) The Continuing Validity of the Law. The law does three things. It expresses the character of God and His will for man’s life. Further, it teaches us the true character of man. God’s intention for man is that he live in accordance with the law of the Lord. Thirdly, the law teaches us the character of salvation. If a life conformed to God’s law is God’s intention for man, then when we are restored to fellowship with Him and live in His will (which is what salvation involves), we will begin to fulfill His intention. In Paul’s words, the requirements of the law will be fulfilled in us as we walk according to the Spirit. Rather than contradict the gospel, the law of God, properly understood, goes hand in hand with it. Whatever else Jesus may have said about the law, He made it plain that He had not come to abolish it.
(2) The Present Fulfillment of the Law. Jesus shows us what the promises of the Old Testament really meant. Jesus says the same is true of God’s law. In 5:17, Jesus is teaching that if we want to know what the law really means, we must look at Him and what He does with it because He fulfils, or ‘accomplishes,’ the law. How? Jesus fulfils the law in His doctrine, or teaching. He brings out the real significance of God’s commands. The Pharisees’ traditional interpretations of the law weakened its power to search the motives of men’s hearts. It was only in the exposition of Jesus that the real power of God’s law could be felt. Jesus did not weaken the law. On the contrary, He let it out of the cage in which the Pharisees had imprisoned it, allowing it to pounce on our secret thoughts and motives, and tear to pieces our bland assumption that we are able to keep it in our own strength.
Jesus fulfils the law in His deeds and lifestyle. He shows the real meaning of the law. The law of God was not a burden on Jesus’ shoulders; rather, it was written in His heart. Jesus enjoyed doing God’s will. It was ‘meat and drink’ to Him.
Jesus fulfils the law in his death. Jesus shows the reality of the law’s holiness as He bears the penalty of our breaking the law by taking our place before the judgment seat of God. It is really at the Cross alone that we discover the real meaning of the curse and judgment of God’s broken covenant. His cry of God-forsakenness, which pierced the darkness of the afternoon of His crucifixion, really says to us: ‘This is the penalty of the broken law. This is the meaning of God’s law.’
Jesus fulfils the law in His disciples. Jesus fulfils the law by writing it in the hearts of His disciples, through the ministry of His Spirit. This lies at the heart of the promise of the new covenant. As we walk by the Spirit, we fulfill the desires of the Spirit, not the desires of the flesh [Gal. 5:16]. We do what the law requires [
(3) The Deep Spirituality of the Law. For I say to you that unless your righteousness surpasses that of the scribes and Pharisees, you will not enter the kingdom of heaven. [5:20]. What did Jesus mean? Jesus Christ not only justifies us by sharing with us His righteousness; He also sanctifies and transforms us by making us righteous. In other words, our righteousness really must surpass that of the Pharisees. For if we are not more righteous than they are, we are not righteous at all. The verses that follow [5:21-48] illustrate what Jesus meant. Pharisaic righteousness was skin deep; Christian righteousness is to be real. It is to be true heart conformity to the law of God. Our obedience to the law is not to be merely external and ceremonial, but real and spiritual. This is the practical fulfillment of the law that marks Jesus’ disciples. They understand that the law is spiritual [Rom 7:14]. They respond to it, not in their own strength, but in the power of the Spirit, who cleanses and renews their hearts.
(4) The Distinguishing Function of the Law. [5:19] Our attitude to the law of God is an index of our attitude to God Himself. If we treat the law lightly and encourage others to do so (if we have a settled and consistent attitude of antagonism toward it), we show that we are strangers to the promise of the new covenant in Christ. But if we love and keep even the least of the Lord’s commandments, and we encourage others to do so as well (if we have a settled attitude of obedience), that is a sure mark that we love Christ and belong to His kingdom. The law is not the basis on which we merit salvation, but it does provide a test to distinguish between those who belong to the kingdom of salvation and those who are outside of it. It is the real test of whether we have been ‘born again’ or not. If we have been, then God’s law has been written in our hearts, and we obey it joyfully.
Questions for Discussion:
1. What did Jesus mean when he said that Christians are the salt of the earth and light of the world? What does this say about the world? How can we bring flavor or zest to the world [see Col. 4:6 and Eph. 4:29]?
2. Our good works (obedience to God’s law) do not give us a right relationship with God. Only Christ can do that. Our salvation is entirely of grace. So what then is the role of good works in our spiritual lives? How do our good works function as light to the world? What message should our good works be sending to the world?
3. In what ways does Jesus fulfill the Law?
4. Think about the statement: “Our attitude to the law of God is an index of our attitude to God Himself”. What is your attitude towards God’s law? What was Jesus’ attitude towards God’s Law?
5. What did Jesus mean “that unless your righteousness surpasses that of the Pharisees and the teachers of the law, you will certainly not enter the kingdom of heaven”? What is the “righteousness” that Jesus expects of His disciples? What role does Jesus and the Holy Spirit play in the believer living a righteous life?
Jesus’ Sermon on the Mount , D.A. Carson, Global Christian Publishers.
The Sermon on the Mount, Sinclair Ferguson, Banner of Truth.
Christian Counter-Culture, John Stott, Inter-Varsity Press.