Ye are the light of the world. It means something to be a Christian. It has many uses. In Jesus time salt was primarily used as a preservative. There was no refrigeration.
Salt is also a chemical compound.
Here in the midwest we use salt on our roads in the winter to melt ice and snow. So, salt is a seasoning, and a preservative that can eat right through steel. It means something to be a Christian. And I believe the words that Jesus spoke in Matt. It means something to be a Christian.