I'm still researching salt! Who'd ever have thought there was so much to learn about salt. As I said before one of the reasons salt takes on so much symbolic meaning is because it sustains life. I could write a book about that (someone already has!), but the bottom line is that water and salt regulate all metabolic functions of the body. Without salt we would die.
The lists of all that salt does in the body is amazing, but let me just share a few of the things I've found.
acidity from the body's cells, particularly the brain cells;
balances the sugar
levels in the blood;
generates hydroelectric energy in your body's cells;
conductivity in nerve cells for communication and information processing;
absorption of nutrients through the intestinal tract;
clears mucous and sticky
phlegm in the lungs and sinuses;
body with a natural antihistamine;
is an anti-stress element
for the body;
helps prevent muscle cramps;
So when the Savior tells us to be the salt of the earth, it includes the fact that we should help sustain life in any and every way we can.