Other than air and water, salt is the most important need for our physical well-being. Animals will travel miles for it. It was one of the earliest commodities to be traded in human society. If salt were to lose its potency that would indeed be a disaster. So, while being compared to salt may not seem very glamorous, it is a very big deal. (Mt 5:13-16)
And that city on a hill top. It’s a very powerful metaphor, much used and abused in the American consciousness, at least in recent years. It was originally used by a colonist even before he arrived in America, before there even was an America. John Winthrop delivered his sermon to his fellow puritan refugees in Southampton before embarking for the Massachusetts Bay Colony in 1630 (see Wikipedia article). It was immediately forgotten, rediscovered in 1838, and forgotten again until much more recently. Since being reused (with attribution) by JFK, and subsequently by Ronald Regan, Barack Obama, and others, it has become something of a shorthand for how special the US is.
The only way in which Winthrop thought his little group was special was that everybody would be watching and so they better not mess up. This was a rather unchristian hubris and historically untrue, since most people at the time couldn’t care less what happened to these troublesome puritans if they only would disappear as far away as possible. Nowadays people doubtless do notice and care, but the Gospel still cannot be used to lay claim to the superiority of any country or earthly arrangement of human affairs.
The prophecy of Isaiah (Is 58:7-10) and of Jesus, as told by Matthew (Mt 5:13-16), is not that we are, in ourselves, something special – like salt or a light on a hilltop. Rather they invite us to understand where does that savor and illumination come from? Not from us, but from God. To switch to a celestial metaphor, our light is like the light of the moon. The moon in fact has no light, it simply reflects the light of the sun.
So it is, when we behave in accordance with God’s commands then His light is reflected in us. As Isaiah explains it, that light shines for us: “then light shall rise for you in the darkness, and the gloom shall become for you like midday” and through us: “Then your light shall break forth like the dawn”. Our role in this is not to boast of how special we are (remember what Paul told us last week) but to “Share our bread with the hungry, shelter the oppressed and the homeless, clothe the naked”. Then we will become a mirror for the one who said: “I am the light of the world” (Jn 8:12). If we walk with the Lord then we will have his light, and others “may see our good deeds and glorify our heavenly Father.”