For this reason many ancient people praised their god or gods for the gift of salt. In our text Jesus identifies His followers as salt. Earth, in this instance, means man or humanity. Everyone listening to Jesus knew salt to be important and valuable. So Jesus was saying His followers are important and valuable people.
Christians are the salt of the earth.
This means that in the world of men the followers of Christ have two essential things to do. The first thing we do as the salt of the earth is hold back or prevent decay. Just as salt in the ancient world was the only thing which prevented food from spoiling or going rotten so the Christian, empowered by the Spirit, is a barrier between the world of men and complete decay, complete rottenness, and complete destruction. God has chosen to make the Christian His front line of defense against Satan and all evil in the world of men. It is the Christian who is appointed by God to fight against wickedness and all the forces of darkness.