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Kitto's Popular Cyclopedia of Biblial Literature
Salt was procured by the Hebrews from two sources: first, from rock-salt, obtained from hills of salt which lie about the southern extremity of the Dead Sea; and secondly, from the waters of that sea, which overflowing the banks yearly, and being exhaled by the sun and the heat, left behind a deposit of salt both abundant and good.
From it is clear that salt was used as a condiment with food. Salt was also mixed with fodder for cattle (). As offerings, viewed on their earthly side, were a presentation to God of what man found good and pleasant for food, so all meat-offerings were required to be seasoned with salt (). Salt, therefore, became of great importance to Hebrew worshippers; it was sold accordingly in the temple market, and a large quantity was kept in the Temple itself, in a chamber appropriated to the purpose. The incense, 'perfume,' was also to have salt as an ingredient (; marginal reading 'salted'), where it appears to have been symbolical, as well of the divine goodness as of man's gratitude, on the principle that of every bounty vouchsafed of God, it became man to make an acknowledgment in kind.
As salt thus entered into man's food, so, to eat salt with any one, was to partake of his fare, to share his hospitality; and hence, by implication, to enjoy his favor, or to be in his confidence. Hence, also, salt became an emblem of fidelity and of intimate friendship. At the present hour the Arabs regard as their friend him who has eaten salt with them, that is, has partaken of their hospitality. The domestic sanctity which thus attached itself to salt was much enhanced in influence by its religious applications, so that it became symbolical of the most sacred and binding of obligations. Accordingly 'a covenant of salt' was accounted a very solemn bond (;; ): a signification to which force would be given by the preservative quality of salt.
But salt, if used too abundantly, is destructive of vegetation and causes a desert. Hence arose another class of figurative applications. Destroyed cities were sown with salt to intimate that they were devoted to perpetual desolation (); salt became a symbol of barrenness (; ); and 'a salt land' () signifies a sterile and unproductive district ().
We have reserved to the end reference to a singular usage among the Israelites, namely, washing new-born infants in salt water; which was regarded as so essential that those could have hardly any other than an ill fate who were deprived of the rite (). The practice obviously arose from a regard to the preserving, the domestic, the moral, and the religious uses to which salt was applied, and of which it became the emblem.
Kitto, John, ed. Entry for 'Salt'. "Kitto's Popular Cyclopedia of Biblial Literature". https://www.studylight.org/encyclopedias/eng/kbe/s/salt.html.