“You are the salt of the earth. But if salt loses its flavor, how can it be made salty again? It is no longer good for anything except to be thrown out and trampled on by people. You are the light of the world. A city located on a hill cannot be hidden.
I came across this quote from Craig Blomberg in the New American Commentary:
Both metaphors of salt and light raise important questions about Christian involvement in society regarding all forms of separatism or withdrawal. We are not called to control secular power structures; neither are we promised that we can Christianize the legislation and values of the world. But we must remain active preservative agents, indeed irritants, in calling the world to heed God’s standards. We dare not form isolated Christian enclaves to which the world pays no attention.