“You are the salt of the earth, but if salt has lost its taste, how shall its saltiness be restored? It is no longer good for anything except to be thrown out and trampled under people’s feet. You are the light of the world. A city set on a hill cannot be hidden. Nor do people light a lamp and put it under a basket, but on a stand, and it gives light to all in the house. In the same way, let your light shine before others, so that they may see your good works and give glory to your Father who is in heaven.” Matthew 5:13-16

Every Lord’s Day I conclude our worship service by reminding us before the benediction that our Triune God sends us out into the world as salt and light. These metaphors are taken from Jesus’ words to his disciples in the Sermon on the Mount. But what do they mean?

In last month’s edition of Grace Notes, I explained that when Jesus says his followers are the “salt of the earth,” he is referring to the fact that as salt preserves food, Christians have a preserving influence in society. Herman Ridderbos, in his commentary on the Gospel of Matthew, explains that as Christians we “counteract the corruption and decay that is at work in the world” because of sin. Each of us has influence over others in our families and in our communities, and as we seek to live according to God’s Word and for his glory, we effectively curb the evil that is among us. But what about light? In what sense are we “the light of the world”?

In the Bible, “light” describes God and the true knowledge of him. “God is light, and in him is no darkness at all” (1 John 1:5). Therefore, to truly know God is to know the life and salvation that he gives. David writes in Psalm 36:9, in his address to God, “For with you is the fountain of life; in your light do we see light.” To “see light” means to experience life, and this is in stark contrast with those who die in unbelief and “will never again see light” (Psalm 49:19). We cannot, therefore, experience life—either physical or spiritual—without God.

This is why Jesus’ declaration in John 8:12, “I am the light of the world,” is a declaration of his divinity. He is God the Son, the great light who has come to the people living in darkness (Matthew 4:16). So when Jesus refers to Christians as the “light of the world,” he is referring to the fact that we are to bring the light of salvation to those living in darkness. We are not a light unto ourselves—we have received the light of Christ by grace through faith, and we are now called to transmit his light to those around us through our words and deeds. William Hendriksen, in his commentary on the Gospel of Matthew, explains this using a helpful modern example:

The light-possessors become light-transmitters. Believers are ‘the light of the world’ in a secondary or derived sense. Christ is ‘the light lighting’ (1 John 1:9). They are the light lighted. He is the sun. They resemble the moon, reflecting the sun’s light. Apart from Christ they cannot shine. The electric bulb does not emit light all by itself. It imparts light only when connected and turned on, so that the electric current generated in the power-house is transmitted to it. So also as long as Christ’s followers remain living in contact with the original light they are a light to others (John 15:4-5). [Therefore] the primary duty of the church remains the spreading forth of the message of salvation, that the lost may be found, those found may be strengthened in the faith, and God may be glorified.

It is amazing to think about how little light is needed to dispel the darkness in a room. Even a small candle provides enough light to read and to work, to find one’s way around a dark house, and to make one feel like the darkness is not unconquerable. We might feel like our words and deeds are weak and ineffective in this dark world of sin, but even the seemingly small, ordinary, and consistent obedience that we show to Christ will be used mightily by the Lord.

Sinclair Ferguson, in his book, The Sermon on the Mount, provides a fitting exhortation and conclusion:

The regeneration of people’s lives is a sovereign work of God’s grace. We cannot bring anyone to newness of life. But it is our responsibility to live the new life in order that others may be challenged by it. It is our responsibility to shine for Jesus Christ so that others will see his salvation expressed in the flesh-and-blood reality of our lives. This is the point Jesus is making: we have a responsibility to show the Christ-like life of light to those around us. We cannot hide it under a cover. Fulfilling this plan will demand that the whole of our lives be whole-heartedly and unceasingly devoted to him and to his service. That devotion will cost us everything. But surely those who are ‘the light of the world’ will give nothing less for him who is the light that the darkness can never overcome (John 1:5).