Question: "What does it mean that believers are to be salt and light (Matthew 5:13-16)?"
Answer: Jesus used the concepts of salt and light a number of different times to refer to the role of His followers in the world. One example is found in Matthew 5:13: “You are the salt of the earth. But if the salt loses its saltiness, how can it be made salty again? It is no longer good for anything, except to be thrown out and trampled by men.” Salt had two purposes in the Middle East of the first century. Because of the lack of refrigeration, salt was used to preserve food, especially meat which would quickly spoil in the desert environment. Believers in Christ are preservatives to the world, preserving it from the evil inherent in the society of ungodly men whose unredeemed natures are corrupted by sin (Psalm 14:3; Romans 8:8).
Second, salt was used then, as now, as a flavor enhancer. In the same way that salt enhances the flavor of the food it seasons, the followers of Christ stand out as those who “enhance” the flavor of life in this world. Christians, living under the guidance of the Holy Spirit and in obedience to Christ, will inevitably influence the world for good, as salt has a positive influence on the flavor of the food it seasons. Where there is strife, we are to be peacemakers; where there is sorrow, we are to be the ministers of Christ, binding up wounds, and where there is hatred, we are to exemplify the love of God in Christ, returning good for evil (Luke 6:35).
In the analogy of light to the world, the good works of Christ’s followers are to shine for all to see. The following verses in Matthew 5 highlight this truth: “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” (Matthew 5:14-16, NASB). The idea here is similar—the presence of light in darkness is something which is unmistakable. The presence of Christians in the world must be like a light in the darkness, not only in the sense that the truth of God’s Word brings light to the darkened hearts of sinful man (John 1:1-10), but also in the sense that our good deeds must be evident for all to see. And indeed, our deeds will be evident if they are performed in accordance with the other principles which Jesus mentions in this passage, such as the Beatitudes in Matthew 5:3-11. Notice especially that the concern is not that Christians would stand out for their own sake, but that those who looked on might “glorify your Father who is in heaven” (v. 16, KJV).
In view of these verses, what sorts of things can hinder or prevent the Christian from fulfilling his or her role as salt and light in the world? The passage clearly states that the difference between the Christian and the world must be preserved; therefore, any choice on our part which blurs the distinction between us and the rest of the world is a step in the wrong direction. This can happen either through a choice to accept the ways of the world for the sake of comfort or convenience or to contravene the law of obedience to Christ.
Mark 9:50 suggests that saltiness can be lost specifically through a lack of peace with one another; this follows from the command to “have salt in yourselves, and be at peace with each other.” And in Luke 14:34-35, we find a reference to the metaphor of salt once again, this time in the context of obedient discipleship to Jesus Christ. The loss of saltiness occurs in the failure of the Christian to daily take up the cross and follow Christ wholeheartedly.
It seems, then, that the role of the Christian as salt and light in the world may be hindered or prevented through any choice to compromise or settle for that which is more convenient or comfortable, rather than that which is truly best and pleasing to the Lord. Moreover, the status of salt and light is something which follows naturally from the Christian’s humble obedience to the commandments of Christ. It is when we depart from the Spirit-led lifestyle of genuine discipleship that the distinctions between ourselves and the rest of the world become blurred and our testimony is hindered. Only by remaining focused on Christ and being obedient to Him can we expect to remain salt and light in the world.