Today if we say someone is “the salt of the earth,” we understand that person to be solid and dependable, someone who can be counted on through thick and thin. We might also say that someone’s speech is salty to mean that their language is coarse, like that of a sailor who has been out to sea for a long time and has not had to be concerned about using polite expressions in refined company. But when Jesus said to his disciples that they were the salt of the earth, they might have understood the metaphor in light of several biblical connotations.
First, salt was a critical necessity for human life, along with water, fire and iron, as Sir 39:26 states. Salt was important for seasoning and preserving food. Job questions, “Can a thing insipid be eaten without salt?” (Jb 6:6).
A second way in which salt was important was for liturgical functions. It was included with cereal offerings (Lv 2:13) and burnt offerings (Ez 43:24). Blending salt with incense kept the fragrant powder pure and sacred (Ex 30:35). Salt was what Elisha used to purify a polluted spring of water (2 Kgs 2:19-22). In Catholic liturgical tradition, the baptismal ritual included putting salt on the infant’s tongue as a symbol of incorruptibility.
Another way in which salt was used was to ratify covenants (Nm 18:19; 2 Chr 13:5). As a preservative, salt symbolized the lasting nature of the agreement.
Finally, different kinds of salts are necessary for the soil to be fruitful, but soil that is “nothing but sulphur and salt” is a desert wasteland (Dt 29:22; Ps 107:34; Jb 39:6). As a symbol of permanent destruction, conquerors would spread salt on a city they had razed (Jgs 9:45). As Jesus called his disciples “salt,” they may have understood any of these meanings: they season and purify the world with God’s love, giving witness to divine fidelity that preserves life for all eternity.
Jesus then queries, “But if salt loses its taste, with what can it be seasoned?” It seems like a trick question. Salt can be diluted, but could it ever lose its taste entirely? It is possible that Jesus was quoting an ancient proverb to which his disciples would respond, “Impossible!” In the Talmud there is an account of Rabbi Joshua ben Hananya (ca. 80-120 C.E.), who was asked by philosophers in the Atheneum at Rome, “If salt becomes savorless, with what can it be salted?” He responded, “With an after-birth of a mule” (b. Bek. 8b). The point is that just as it is impossible for a mule to give birth or for salt to become insipid, so disciples cannot cease to be who they are and to season the world with the good news.
The accompanying image of disciples as light reinforces the message. As impossible as it is for a city set on a mountain to be hidden, and as unthinkable as wasting fuel to light a lamp only to extinguish it immediately, so inconceivable is it that disciples would cease to let their light shine before others. Although trials and tribulations may threaten to dilute disciples’ “saltiness” or dim their light, nothing is ever able to take away their capacity to illumine God’s love for others.
Finally, salt and light are most effective when they do not call attention to themselves. Just as in well-seasoned food the salt is not noticeable and in a properly lit room the lamps are not the focus of attention, so disciples’ good deeds do not redound to themselves but lead others to glorify God.