Mathew 5:13 “You are the salt of the Earth. But if the salt loses it saltiness, how can it be made salty again? It is no longer good for anything, except to be thrown out and trampled under foot.”
It’s saying if a seasoning has no flavor, it has no value. If Christians make little to no effort to affect the world around them, there are of little value representing God‘s presence in this world. If we are too much like the world we won’t be able to help or change it; as seasoning, we will be worthless. Christians should not blend in with everyone else. But if we isolate ourselves from non-Christians we lose the ability to reach them. Instead, we should influence others positively just as seasoning, brings out the best flavor in food.