Q From Aleda and Ian Turnbull: If someone is the salt of the earth they have admirable qualities and in particular can be relied upon. Why is this when salt added to the earth makes it sterile?
A The expression is Biblical and comes from Matthew, 5:13. From the King James Bible of 1611: “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.”
Salt has always been one of the most prized commodities, essential both for life and for preserving food. Roman soldiers were paid an allowance to buy salt, the origin of our salary. A man worth his salt is efficient or capable. To eat salt with someone was to accept his hospitality and a person who did so was bound to look after his host’s interests. The Bible also speaks of a covenant of salt, one of holy and perpetual obligation. Newborn children were anciently rubbed with salt to protect them against evil forces.
To Jesus, therefore, salt of the earth was a great compliment. To understand his comment fully, though, you have to know a bit about where Jews of his time got their salt. Some came from saltpans on the margins of the Dead Sea, but much was obtained from Mount Sodom (Jebel Usdum in Arabic), a ridge of limestone and rock salt at the south-west corner of the Dead Sea (a pillar of salt here is said to have given rise to the legend of Lot’s wife). This rock salt was the literal salt of the earth. Because the deposit’s outer layer was exposed to the elements, it became contaminated and its salt content depleted by weathering, losing its taste and value, so becoming good for nothing.
The use of salt to poison the ground is entirely separate.