In the Bible, salt means at least three things. It makes food tasty, it preserves food and it used to be a part of the sacrifice made to God. About the last meaning, it says in Leviticus 2:13: “Put salt on every grain offering, because salt represents the covenant between you and God. You must put salt on all your offerings.” So in the Bible you read many times about the role of salt in relation to the covenant between God and the people.
About the tastiness Job 6: 6 says: “Can that which is unsavory be eaten without salt? Or is there any taste in the white of an egg?”
Salt of the world
Later on, Jesus tells His disciples that they are the salt of the world (Matthew 5:13). If they are not making any difference in the world, they act like tasteless salt. And you can conclude that the Christians have to go out into the world, out of the salt-shaker, otherwise they can’t do their job. Interpreted in a practical way: followers of Christ are there to preserve society from rotting away, to give it taste and to point to God’s covenant.