Most people of Jesus' time probably thought of salt in terms of its preservative characteristic. As people have studied salt over the years we have learned it is both a preservative and much more.
Royal Society of Chemistry, London, says:
"Why do we need salt? It is the sodium (ions) present in salt that the body requires in order to perform a variety of essential functions. Salt helps maintain the fluid in our blood cells and is used to transmit information in our nerves and muscles. It is also used in the uptake of certain nutrients from our small intestines. The body cannot make salt and so we are reliant on food to ensure that we get the required intake." http://www.rsc.org/get-involved/hot-topics/Salt/do-we-need-salt.asp
If the the world needs feeding with spiritual salt the same way that the human body needs physical salt, what answer comes back when we Christians ask ourselves:
"How does my life, how does the church's life measure up to the Lord's description of us as salt?"