A follower of Jesus Christ is essentially different from everyone else.
The emphasis of Jesus’ statement - “You are the salt of the earth” - is that “You, and you alone, are the salt of the earth.”
Only Christians are the salt of the earth.
What this says about the world
It means the world is sinful and rotten. What is in this world is totally different from who the Father is.
Do not love the world or the things in the world. If anyone loves the world, the love of the Father is not in him. For all that is in the world—the lust of the flesh, the lust of the eyes, and the pride of life—is not of the Father but is of the world. And the world is passing away, and the lust of it; but he who does the will of God abides forever. (1 John 2:15-17)
It also means the world is without “flavor” or “tasteless,” so to speak. Life without God is ultimately meaningless.
Being the salt of the earth
In our individual lives - at work, at home, at school - we are “the salt of the earth.” Just by being who we are supposed to be (like Christ), we confront the evil around us.
The world tends to “clean up their act” when they are around a Christian who lives differently from the world. Sometimes people will modify their behavior or words when around a Christian who doesn’t act or talk that way.
Sometimes the world will react rather strongly and persecute Christians (Matthew 5:10-12).
When this happens, the salt of the earth is working on the world.
What this means is that who we are matters (Matthew 5:1-9).
Are we poor in spirit?
Are we mourning over our own sin?
Are we meek?
Are we hungering and thirsting after righteousness?
Are we merciful?
Are we pure in heart?
Are we peacemakers?
This is who a Christian is supposed to be. This is what the life of someone who is the “salt of the earth” will look like.
Do you want to have an impact on the world around you? The first place we must look is at ourselves.