A fundamental necessity of life, salt has been used since ancient times for many different purposes, and is heavily loaded with spiritual meaning.
Salt plays an interesting, often contradictory role in the Bible. Salt is a fundamental necessity of life, and has been used since ancient times in many cultures as a seasoning, a preservative, a disinfectant, a component of ceremonial offerings, and as a unit of exchange. The Hebrews, both during the Old Testament and the New Testament periods, were certainly not an exception.
Leviticus (2:13) and Ezekiel (43:24) make it evident that salt was an important part of ancient Hebrew religious sacrifice. “And every offering of your grain offering you shall season with salt; you shall not allow the salt of the covenant of your God to be lacking from your grain offering. With all your offerings you shall offer salt.” (Leviticus 2:13) Also, salt was always cast on the burnt offering (Ezekiel 43:24), and was part of the incense offered in the Temple (Exodus 30:35). Moreover, even newborn babies were rubbed with salt, as we read in Ezekiel: “As for your nativity, on the day you were born your navel cord was not cut, nor were you washed in water to cleanse you; you were not rubbed with salt nor wrapped in swaddling cloths.” (Ezekiel 16:4)
But salt was also widely and variably used symbolically in ancient Israel. The books of Numbers and 2 Chronicles present salt as the symbol that confirms friendship between parties. Eating salt together, in fact, was (and still is) a sign of friendship in some regions in the Mediterranean.
In the Gospels, we find Jesus calling his disciples “the salt of the earth” (Matt 5:13), yet adding a warning to this claim:
“But if the salt loses its saltiness, how can it be made salty again? It is no longer good for anything, except to be thrown out and trampled underfoot.”
Also, in the Gospel of Mark (Cf. Mk 9:50) Jesus reminds his disciples to “have salt among yourselves, and be at peace with each other.” In this context, “salt” is employed to express the capacity to preserve, purify, and cleanse: just as fire burns away impurity transforming everything into its own substance (that is, consuming it), salt arrests corruption, stops decomposition, keeps off destruction, and preserves whatever is in contact with it. In sum, salt protects from decay. It is clear, then, that Jesus is inviting his disciples to preserve the good will that “seasons” positive relationships between people, and which “protects” the community from being corrupted, “preserving” it in good state.