He was an old salt…
He uses some salty language…
Take it with a grain of salt…
There are several ways of using the word “salt” in various coloquial idioms of our day. Jesus, himself, added to these idioms, telling the disciples that they need to be salty:
Everyone will be salted with fire.
“Salt is good, but if it loses its saltiness, how can you make it salty again? Have salt among yourselves, and be at peace with each other.”
Mark 9:49-50
Jesus had just finished telling his disciples that they need to get rid of anything that causes them to sin. For example, if an eye or a hand causes them to sin, they should pluck it out or cut it off. I don’t think Jesus is being literal as he says these things, although he does tell the disciples that it would be be better to go into heaven maimed rather than go into hell with their full body.
But then he goes on to tell them that they will be salted with fire.
The disciples will be tested. They will be refined. This is the salt that they must have within themselves individually and amongst them as disciples of Christ. They must have been tested and refined. They must have lost all of the dross, all of those things that have come from our flesh instead of from the Spirit of God such that they are now living completely and entirely for Christ. In this way, they will have salt amongst themselves.
On the other hand, Jesus says that if they lose their saltiness, they are of no good whatsoever to God. Within the kingdom of God, they will not be worth anything. They will have just become like the people of the world. They will not be demonstrating anything within the kingdom. They will instead simply be just like everyone else. No salt, no refinement. Just like the world.
So Jesus says that we need to be salty. We need to be creatures of the kingdom of God. We need to be people who are set apart from the world. We need to be salty.