What does it mean that believers are to be salt and light (Matthew 5:13-16)?

"Ye are the salt of the earth" — they were the real preservative principle there: all the rest, the Lord intimates, were good for nothing. But, let us note, He gives a solemn warning that there is a danger that the salt should lose its savour. He is not now speaking of the question whether a saint can fall away or not. People go with their own questions to Scripture, and pervert the word of God to suit their previous thoughts. The Lord is not raising the question whether life is ever lost; but He is speaking of certain persons who are in a given position; and among them there may be persons who take it heedlessly, or even falsely, and then comes the fading away of all that they had once possessed. He announces their judgment — a most contemptuous one — to be passed upon that which took so high a place without reality.

"Ye are the light of the world." This is another thing. Bearing in mind the distinction drawn in the series of the beatitudes and of the persecutions, we have the key to these two verses. The salt of the earth represents the righteous principle. This evidently involves the clinging to the eternal rights of God and the maintenance before the world of what is due to His character; but it is gone when that which bears the name of God falls below what even men think proper, and they scoff against what is called religion. All respect vanishes, and men think that the condition of Christians is a fair subject for ridicule. But now, in verse 14, we have not only the principle of righteousness, but of grace — the outflowing and strength of grace. And here we find a new title given to the disciples, as descriptive of their public testimony — 'the light of the world." The light is clearly that which diffuses itself. The salt is what ought to be inward, but the light is that which scatters itself abroad. "A city that is set on a hill cannot be hid." There was to be a diffusion of its testimony around. Man does not light a candle to put it under a corn measure, but on a candlestick, "and it giveth light unto all that are in the house." After this manner let your light shine before men, "that they may see your good works, and glorify your Father which is in heaven." Mark it well.

We have looked at these two striking sketches of the testimony of believers here below as the salt of the earth, the preservative energy in the midst of profession; and as the light of the world going out in the activities of love toward the poor world; and the danger of the salt losing its savour, and of the light being put under a bushel. Now we find the great object of God in this twofold testimony. It is not merely a question of the blessing of souls, for there is not a word about evangelizing or saving sinners, but of the walk of saints. There is a grave question that God raises about His saints, and this is about their own ways apart from other people. Calls to the unconverted we find abundantly elsewhere, and none can exaggerate their importance for the world; but the sermon on the mount is God's call to the converted. It is their character, their position, their testimony distinctively; and if others are thought of throughout, it is not so much a question of winning them, as of the saints reflecting what comes from above. This light is what comes from Christ. It is not, Let your good works shine before men. When people talk about this verse thinking of their own works, they are generally not good works at all; but even if they were, works are not light. Light is that which comes from God, without admixture of man. Good works are the fruit of its action upon the soul; but it is the light which is to shine before men. It is the confession of Christ that is the point before God. It is not merely certain things to be done. The light shining is the great object here, though doing good ought to flow from it. If I make doing good everything, it is a lower thought than that which is before the mind of God. An infidel can feel that a shivering man needs a coat or a blanket. The natural man may be fully alive to the wants of others; but if I merely take these works and make them the prominent aim, I really do nothing more than an unbeliever might. The moment you make good works the object, and their shining before men, you find yourself on common ground with Jews and heathen. God's people are apt thus to destroy their testimony. What so bad, in the way of a thing done professedly for God, as a work that leaves out Christ, and that shows a man who loves Christ to be on comfortable terms with those that hate Him? This is what the Lord warns the saints against. They are not to be thinking about their works, but that the light of God should shine. Works will follow, and much better works than where a person is always occupied with them. "Let your light so shine before men, that they may see your good works, and glorify your Father which is in heaven " (ver. 16). Let your confession of what God is in His nature and of what Christ is in His own person and ways — let your acknowledgment of Him be the thing that is felt by and brought before men; and then, when they see your good works, they will glorify your Father which is in heaven. Instead of saying, What a good man such a one is, they will glorify God on his behalf — connecting what you do with your confession of Christ.

The Lord now uses two striking figures to show what His own should be in His absence. "Ye are the salt of the earth: but if the salt have lost his savour, wherewith shall it be salted? it is thenceforth good for nothing, but to be cast out, and to be trodden under foot of men. Ye are the light of the world. A city that is set on an hill cannot be hid. Neither do men light a candle, and put it under a bushel, but on a candlestick; and it gives light to all that are in the house. Let your light so shine before men, that they may see your good works, and glorify your Father which is in heaven" (vers. 13-16). "Ye are the salt of the earth." Now salt is preservative, it preserves from corruption. When the saints are taken out of the earth there will be nothing left but the dead carcase of a Christless Christendom, nothing but corruption. Salt answers to righteousness. But "Ye are the light of the world," gives another thought. Light answers to grace. Salt merely preserves things pure from corruption, but light is aggressive, it drives out the darkness. So grace goes forth outside and seeks. "It gives light."

A Christian should be a candle, and what for? That his light may be seen, and the Father get the glory. The Lord is very careful not to say, Let your good works be seen, but, Let your light so shine, and why? What is your light? It is the life of Christ reproduced in you, and that being seen, it is Christ in you that is seen. That is the point. The world is to see Christ in you. It is not merely giving a testimony, but being a testimony. Not being a light-bearer, but being light; and so your Father gets the glory, for that is all Christ. The reflection of Christ in the life of a saint has this for its effect, men will glorify your Father which is in heaven.

The salt of the earth is a different thing from the light of the world. The earth, it appears to me, expresses that which already professed to have received light from God — that which was in relationship with Him by virtue of the light — having assumed a definite shape before Him. The disciples of Christ were the preservative principle in the earth. They were the light of the world, which did not possess that light. This was their position, whether they would or no. It was the purpose of God that they should be the light of the world. A candle is not lighted in order to be hidden.

In ancient times salt was the most important agent for seasoning and preserving foods. Salt is pungent, bitter; but it keeps what is good and prevents corruption. In the Old Testament, the "salt of the covenant" had, on God's order, to be added to all sacrifices (Lev. 2: 13). Thus salt is a clear symbol of the sanctifying, keeping power of God which should be expressed in us. We are not sugar or honey, but the salt of the earth. If we witness mockery concerning divine things at school, at work or in other situations and we do not ignore it, but reprimand the scoffers in the right way, and if we do not laugh at certain jokes, then we are the salt of the earth. Often our mere presence will exercise a moderating influence on unbelievers. Two further passages make clear that this "salt" should not be confounded with human pungency or even cutting remarks. The Lord says in Mark 9: 50 to His disciples: "Have salt in yourselves, and be at peace with one another." Paul writes to the Colossians: "Let your word be always with grace, seasoned with salt." (Colossians 4: 6) Grace and peace therefore are not opposed to salt but complementary to it.

Our Lord says, “As long as I am in the world, I am the light of the world” (John 9:3). But in view of His absence His saints are said by Him to be the “light of the world” (Matt. 5:14; Phil. 2:15). Saints are light in the Lord (Eph. 5:8), because they are here to present the moral characteristics of Christ to the gaze of men who are in darkness, and because all the source and power of their light resides in the Lord of heaven, who is hidden from the world, but in faith and in the Spirit manifest to His own. The moon shines during the night because it is in the light of the sun, and saints shine during the absence of Christ because they are in the light of the risen Son of God.

On the other hand, as the light of the world we are the reflection of Christ (Jn.8:12). Our testimony to Him is not to be hid. As a city set on a hill, the disciples formed a company above the common level of the world, and as such will necessarily draw the attention of the world. A lamp too is not to be put under a bushel measure, that is, obscured by that which speaks of man's work. Let us not allow our work to get in the way of the light of Christ, who is the only source of light for darkened men. The lamp set in its proper place will give light to all who are in its Vicinity.

In verse 16 the light is distinct from good works, but both are closely connected. The light speaks of moral and spiritual testimony to Christ. The good works are works that back up this testimony as being real. Apparent good works by themselves would draw attention to the person who does them, that he might be honored; but if the light of testimony for Christ accompanies the good works, this influences others to recognize that God our Father is the source of the works and therefore to glorify Him in heaven, the place of highest authority.

Thus the positive part of our Lord's teaching embraces the promises (as v. 5) for the earth, and for the heavens the verses already referred to. Others apply generally to the spirit desired by God, which, at bottom, is the character of Christ Himself. The disciples were set as the salt of the earth (of that which was in relation with God) in contrast with every corruption, and as the light of the world, the testimony of God to those who lay in the dark outside. Their testimony ought to be clear enough for men to know to what they should attribute the fruits manifested in them. The place of the disciples was thus sketched clearly, the remnant called by grace.

Here the character of the position for the disciples goes beyond "the salt of the earth." For this was expressive of righteousness; a righteousness not outward like that of the scribes and Pharisees (which sought reputation of man, and was little beyond the pride of a Stoic), but lowly and real as in God's sight. Whereas "the light of the world" is the shining forth of grace, and inseparable from the confession of Christ in that respect. Salt preserves, but does not make everything manifest as the light does.

"Ye are the light of the world: a city set upon a hill-top cannot be hid. Nor do they light a lamp, and put it under the dry measure but on the lamp-stand, and it shineth unto all that are in the house. Thus let your light shine before men, so that they may see your good works, and glorify your Father that is in the heavens" (vers. 14-16).

Salt is the righteously preservative principle. It is sharp rather than sweet, but guards from impurity and decomposition. It gives fixity to what is good and wholesome. It proves all things, and holds fast the right. It keeps aloof from every form of wickedness. When then the disciples are called the salt of the earth, the Lord designates them as set apart to God the Father, and in patient continuance of good work seeking for glory and honour and incorruptibility at Christ's coming. They obey the truth, and are to hold fast what they have till then. If they lose the good savour, it is fatal. Saltless salt (and such a change was familiar in those lands) cannot be restored. It is not fit for anything but to be trodden down on the streets, as it often was.

This is in reference to the first beatitudes. Salt preserves from corruption. Thus is the heir of the kingdom to be in the midst of all that which is corruption. But what when the salt becomes insipid? It becomes absolutely worthless and is trodden under foot. It was so with Jerusalem , it has become worthless; it has been trodden down by the Gentiles and Christendom will be that, nay is, in the age of Laodicea . Ye are the Light of the world. This is in reference to the last three beatitudes. This is followed by the exhortation: "Let your light thus shine before men so that they may see your upright works, and glorify your Father who is in the heavens." But what light is it which is to shine? Surely this can mean only the reflection of Him who is the Light. "He does not say let your good works shine, but let your light shine; that is, let Christ shine in your life; not that ye may see your good works, but that men see them; not to your glory, but to the glory of your Father."