God appointed that salt should be used in all the sacrifices that were offered to him, Leviticus 2:13 . Salt is esteemed the symbol of wisdom and grace, Colossians 4:6; Mark 9:50 : also of perpetuity and incorruption, Numbers 18:19; 2 Chronicles 13:5 . The orientals were accustomed also to ratify their federal engagements by salt. This substance was, among the ancients, the emblem of friendship and fidelity, and therefore used in all their sacrifices and covenants. It was a sacred pledge of hospitality which they never ventured to violate. Numerous instances occur of travellers in Arabia, after being plundered and stripped by the wandering tribes of the desert, claiming the protection of some civilized Arab, who, after receiving them into his tent, and giving them salt, instantly relieves their distress, and never forsakes them till he has placed them in safety. An agreement, thus ratified, is called, in Scripture, "a covenant of salt." The obligation which this symbol imposes on the mind of an oriental, is well illustrated by the Baron du Tott in the following anecdote: One who was desirous of his acquaintance promised in a short time to return. The baron had already attended him half way down the stair case, when stopping, and turning briskly to one of his domestics, "Bring me directly," said he, "some bread and salt." What he requested was brought; when, taking a little salt between his fingers, and putting it with a mysterious air on a bit of breast, he ate it with a devout gravity, assuring du Tott he might now rely on him.
Although salt, in small quantities, may contribute to the communicating, and fertilizing of some kinds of stubborn soil, yet, according to the observations of Pliny, "all places in which salt is found are barren and produce nothing." The effect of salt, where it abounds, on vegetation, is described by burning, in Deuteronomy 29:23 , "The whole land thereof is brimstone, and salt of burning." Thus Volney, speaking of the borders of the Asphaltic lake, or Dead Sea, says, "The true cause of the absence of vegetables and animals is the acrid saltness of its waters, which is infinitely greater than that of the sea. The land surrounding the lake, being equally impregnated with that saltness, refuses to produce plants; the air itself, which is by evaporation loaded with it, and which moreover receives vapours of sulphur and bitumen, cannot suit vegetation; whence that dead appearance which reigns around the lake." So a salt land, Jeremiah 17:6 , is the same as the "parched places of the wilderness," and is descriptive of barrenness, as saltness also is, Job 39:6; Psalms 107:34; Ezekiel 47:11; Zechariah 2:9 . Hence the ancient custom of sowing an enemy's city, when taken, with salt, in token of perpetual desolation, Judges 4:45; and thus in after times the city of Milan was burned, razed, sown with salt, and ploughed by the exasperated emperor, Frederic Barbarossa. The salt used by the ancients was what we call rock or fossil salt; and also that left by the evaporation of salt lakes. Both these kinds were impure, being mixed with earth, sand, &c, and lost their strength by deliquescence. Maundrell, describing the valley of salt, says, "On the side toward Gibul there is a small precipice, occasioned by the continual taking away of the salt; and in this you may see how the veins of it lie. I broke a piece of it, of which that part that was exposed to the sun, rain, and air, though it had the sparks and particles of salt, yet it had perfectly lost its savour; the inner part, which was connected with the rock, retained its savour, as I found by proof." Christ reminds his disciples, Matthew 5:13 , "Ye are the salt of the earth; but if the salt have lost its 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." This is spoken of the mineral salt as mentioned by Maundrell, a great deal of which was made use of in offerings at the temple; such of it as had become insipid was thrown out to repair the road. The existence of such a salt, and its application to such a use, Schoetgenius has largely proved in his "Horae Hebraicae." The salt unfit for the land, Luke 16:34, Le Clerc conjectures to be that made of wood ashes, which easily loses its savour, and becomes no longer serviceable.
Effoetos cinerem immundum jactare per agros.
VIRGIL. Georg. v. 81.
"But blush not fattening dung to cast around, Or sordid ashes o'er th' exhausted ground. WARTON.