You are the salt of the earth TB Beitzah 39

 The Gemara gives three reasons why a small amount of salt and spices mixed in with the flour to make dough isn't annulled. "Abaye said: It is a decree that the Sages made, lest a woman make dough in partnership with her neighbors. Indeed, in the case of the mishna, the small amount she received from her neighbor should be nullified in the dough. However, on another occasion, several friends or neighbors might decide to pool ingredients and prepare bread in partnership, in which case the bread is certainly bound by the Shabbat limits of all the parties combined. In order to prevent confusion between making dough in partnership and making it with borrowed ingredients, the Sages made a decree that the dough in both cases be subject to the same limitations.

“Rava said a different reason: Spices are made in order to add taste to food, and taste is not nullified, even if the amount of actual substance is minute. Nullification indicates that a small amount of food may be considered insignificant and therefore null and void, but if an ingredient is added with the specific intent that its taste be noticed, there can be no nullification.

“And Rav Ashi said a different explanation as to why the spices, water, and salt are not subject to nullification: It is because any one of these ingredients is an object whose prohibition is temporary, as the prohibition against their being taken out of the Shabbat limits lapses once the Festival has passed, and the general principle is that anything whose prohibition is temporary cannot become nullified, even by one part in one thousand." (Sefaria.org translation)

Although salt is a commonplace and inexpensive ingredient today, that wasn't always the case. Before the age of refrigeration, salting meat was a main mode of preservation so the meat would not spoil. It was not as easily acquired. Salt was a dear ingredient. Today the phrase ``you are the salt of the earth” means very good and honest person or group of people. That's not what it meant when Jesus used it in the sermon of the Mount. The phrase derives from Jesus' Sermon on the Mount: “You are the salt of the earth.” (Matthew 5:13) Jesus meant that the common people he was addressing – fishermen, shepherds, laborers – were worthy and virtuous. He was alluding, not to the tang of salt, but to its value. Jesus meant that the common people he was addressing – fishermen, shepherds, laborers – were worthy and virtuous. He was alluding, not to the tang of salt, but to its value.