This verse is considered by many to be the essence of the Sermon on the Mount. The encouragement is directly linked with God's claim on our whole life. In Jesus' days salt was something precious, it was and still is rare. In Africa the sharing of salt has remained part of communal village life right up to the present day. In former times there were Salt Roads, and the wealth of entire regions in Germany was created by deposits of salt.
Salt can preserve and heal, but it cauterises when strewn in an open wound.
This means that these words could appear to cause offence. We could go on elaborating on this picture, making use of all these approaches. Salt can only flavour food that is there already without which it would be inedible. On the other hand, food must not be salted too much. There is no shortage of associations, all of which can form the subject of biblical theological reflection.