“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 underfoot.
“You are the light of the world. A town built on a hill cannot be hidden. Neither do people light a lamp and put it under a bowl. Instead they put it on its stand, and it gives light to everyone in the house. In the same way, let your light shine before others, that they may see your good deeds and glorify your Father in heaven.
Jesus has just given us a series of character traits or attributes in the beatitudes, but so far, we have attributes without a purpose; in these verses, Jesus gets to His larger point.
To illustrate, He uses two metaphors, salt and light. Salt had many uses in the ancient world, thus it is very difficult to nail down the exact use Jesus might have been referring to; He just didn’t say. Over the years, people have chosen a possible use and claimed it as the thing Jesus had in mind, but to be perfectly honest, such a position is only a matter of speculation, so let’s try to avoid falling into that trap; we’ll just look at salt as a basic and useful substance. As an example, I’ll mention what were probably the two most common uses of salt, as a food preservative, and as the basic ingredient for seasoning food. For either of these uses, if the salt loses its saltiness, i.e. its usefulness, then it is worthless. If we, as “the salt of the earth” lose our usefulness, then we might fit into that same category.
This image becomes crystal clear in His next metaphor, light. We, as we exhibit the traits of character that Jesus spoke of in the beatitudes, become the “light of the world.” Imagine if you can, a world filled with the meek, the poor in spirit, peacemakers, and all of the rest of those attributes, next to what we are used to… this is what Jesus meant here by “the light of the world.” Light does no good if it is hidden from view; it’s just like salt that has lost its saltiness, so He tells us to let our light shine forth in this dark world as a contrast to the norm, to the glory of God.
That is what “Kingdom” is all about.
I mention this because the Sermon on the Mount is set in the context of Jesus proclaiming the Kingdom, and these verses wrap up the introduction of the Sermon. If you are looking at it from a structural point of view, the first 16 verses of this chapter set forth the thesis of the rest of Sermon, and as we continue, we will see an expansion upon this theme of bringing about the Kingdom of Heaven on this earth in the here and now.