Salt is the substance with chemical formula NaCl that it consists of Sodium and Chlorine. These two chemical elements are of almost opposite properties (the first is a very active metal and the second is a halogen).
Both are highly reactive and flammable, both are poisons. But when they are combined together they produce an “moderate” substance which we can even to eat in some quantities.
So Jesus speaking about salt meant composition of opposites which lead to a moderate outcome.
(Mark 9:50) “Salt is good, but if the salt has lost its saltiness, with what will you season it? Have salt in yourselves, and be at peace with one another.””
This means to hold seemingly contradictory radical concepts combined into a composite theological theory which makes them into one moderate philosophy leading to peace with one another.
See my book End of Gospel for some examples of such concepts.