You are the salt of the earth, but if the salt becomes dull, what can make it salty again? It is then good for nothing but to be thrown out and trampled down by people. You are the light of the universe; a city cannot be hidden when it stands on a hill. You don’t light a lamp and place it under a bowl, but on the lamp-stand to give light to everyone in the house. Let your light shine out like that before human beings, so that they may see the lovely things you do and celebrate your father who is in heaven.
Salt was used for preserving food, and for seasoning as well as for human health. In the ancient Middle East new born babies were rubbed with salt. In Israel it was obtained by evaporation of brine from pans, as well as by trade, from salt mines. In the Graeco-Roman civilisation salt was a metaphor for liveliness, intelligence, wit. Which use of salt had Jesus in mind as being an image of discipleship? Obviously its use as a preservative, to keep things from going rotten, provides a coherent metaphor for the activity of good people.
The only counter-indication to that is the verb which I have translated “to become dull”- -in Greek “moraino” of which the root meaning is to become “foolish, stupid or dull.” This may point towards the use of salt to give taste, which lies behind its common metaphorical sense of liveliness, piquancy, wit, intelligence. We are not accustomed to thinking of Jesus or his disciples in such terms, but given Jesus’ excellence as a public teacher, including his readiness to engage with all conditions of people, maybe we should be ready to think he wanted his disciples to do the same: that they should be salty not in a smart or superficial manner, but as lively people who could bring life to others.
But how can salt become dull? A Jewish Rabbi around 90 CE mocked the notion that salt can degenerate, by recommending that its saltiness could be restored with the afterbirth of a mule. “How can a mule give birth?” his disciples asked scornfully, remembering that mules are sterile. “How can salt lose its saltiness?” He replied.
True, as long as salt is salt it will do what salt does. But then as now, salt could be adulterated with other chemicals, so that the seller’s profit was increased. This salt could lose its saltiness in time and have to be thrown away. Maybe Jesus was suggesting that his disciples could degenerate if their way of life was adulterated with other allegiances.
We are used to the translation “Light of the world” which is of course possible. But the Greek word is “kosmos” meaning the well-ordered heavens and the earth. Universe is not quite right but it indicates the huge scope of the disciples’ shining. In all the universe however it is human beings who need enlightened.
Jesus’ optimism amazes me. Human beings see good deeds all the time but few take any notice far less celebrate the origin of goodness in God. Still what else can be done to turn people towards God’s goodness? The goodness of the creation may do so, but human goodness is more persuasive. Jesus commends lovely deeds in the face of all cynicism and corruption.