Viewing the 1769 King James Version. Click to switch to 1611 King James Version of Matthew 5:13
Ye are the salt of the earth: but if the salt have lost his savour, wherewith shall it be salted? it is thenceforth good for nothing, but to be cast out, and to be trodden under foot of men.
The human body contains many salts, of which sodium chloride (AKA common table salt) is the major one, making up around 0.4 per cent of the body's weight at a concentration pretty well equivalent to that in seawater. So a 50kg person would contain around 200g of sodium chloride - around 40 teaspoons. Since we lose salt whenever we sweat, it has to be continually replaced.