"It is a covenant of salt, forever before the Lord."2

Salt sustains life. It is essential for digestion and in respiration. Without sodium, which the body cannot manufacture, the body would be unable to transport nutrients or oxygen, transmit nerve impulses, or move muscles, including the heart. An adult human being contains about 250 grams of salt, which would fill three or four salt-shakers, but is constantly losing it through bodily functions. It is essential to replace this lost salt.

Salt preserves. Until modern times it provided the principal way to preserve food. Egyptians used salt to make mummies. This ability to preserve, to protect against decay, as well as to sustain life, has given salt a broad metaphorical importance.

Salt was to the ancient Hebrews, and still to modern Jews, the symbol of the eternal nature of God's covenants with Israel. On Friday nights Jews dip the Sabbath bread in salt. In Judaism, bread is a symbol of food, which is a gift from God, and dipping the bread in salt preserves it—keeps the agreement between God and his people.

Loyalty and friendship are sealed with salt because its essence does not change. Even dissolved into liquid, salt can be evaporated back into square crystals. In both Islam and Judaism, salt seals a bargain because it is immutable.

The search for salt has challenged engineers for millennia.... A number of the greatest public works ever conceived were motivated by the need to move salt. Salt has been in the forefront of the development of both chemistry and geology. Trade routes that have remained major thoroughfares were established, alliances built, empires secured, and revolutions provoked — all for something that fills the ocean, bubbles up from springs, forms crusts in lake beds, and thickly veins a large part of the earth's rock fairly close to the surface.3

1 Mark Kurlansky, Salt, The Penguin Group, 2002: 6-7.
2 The Bible, Numbers 18:19.
3 Kurlansky: 12.