The strength of salt is that it has a very distinctive quality. It is unique because it has a very specific taste, and affects food in a particular way. You can count on it enhancing the flavor of our food, causing certain chemical reactions during baking, and melting snow on sidewalks.
But what happens when salt loses it's saltiness. It is no longer salt. But worse, it can't even be classified as something else. It is essentially nothing — unless you give it some chemical designation that does few people any good. Putting it on your food is like putting on sand. It adds no taste, just gravel. And it is useless for baking or melting snow. It is nothing.
Jesus said that we (believers) are the salt of the earth. But if we lose our saltiness, we aren't good for anything. And worse, we aren't good for anything but to be thrown out and trampled by other people. (Matthew 5:13-16)
Since this is undesirable (or it should be), what does Jesus mean by that? How are we like salt? And how are we like salt that isn't salty?
We are like salt when we hold certain convictions to be true. Our lives reflect these convictions through our attitudes, behavior, and habits. It comes out in the way we speak, and in what we say. We can't help ourselves, and the people around us know it.
But when someone pretends to be salt (hold to certain convictions), but seeks to be friends with the world, are unsalted salt. People like this join with the world in what it hates, likes, honors, and upholds — even when they say they don't. They adjust their behaviors, attitudes, and habits to be acceptable to everyone. And they speak as if they hold certain convictions to be true, and yet say things that directly contradict what they say they believe.
This makes that person seem wishy-washy and their opinion isn't worth much. The friends they long to please hate them for their duplicity. They get no respect from them or their enemies. They become as worthless as their friendship. For a time they may make a lot of "friends". But they do not produce good fruit for God.