Mat 5:13 Ye are the salt of the earth: but if the salt have lost his 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.
You all yourselves are the salt, the valuable wit of the planet. If, however, the wit might become insipid [at some point], in what is going to be gathered together? In nothing is it value except having been thrown to be trampled down beneath people.
This is one of the most complex verses of Christ's words. It blends a number of multiple meanings together and plays on words together. The KVJ translation goes straight to the easiest, most consistent meaning, but that meaning doesn't really work. Nor were these words chosen for their obvious meaning.
The pronoun "you" is used to emphasize it. It is plural, addressing all listeners.
The Greek metaphorical meaning of salt is "wit." So, since Christ was using the term as a metaphor, he is primarily praising people for their cleverness. However, salt had other meanings in Christ's era as well. It was used as money to pay wages. Our word "salary" comes from the Roman word for salt. So Christ might have also been implying that people were valuable, perhaps as a preservative of common sense. The fact that this verse is about knowledge makes its connection to the next verse, Mat 5:14, much clearer.
The word translated as "earth" means "land," "dirt," and the "planet." It is like the English word for "earth" except that it has a little more sense of arable land. A key difference between the next verse and this one is the use of the term "earth" here, which refers to the planet. The next verse uses the term "world" which refers to the world order of men. By using the term for the planet here, Christ is saying the people are the salt of the natural world, the God-made planet, not society. The following verse refers to society (for more on the difference between earth and the world see this article).
The Greek word translated as "lost its savor," means "to act a fool," or, in the passive, as it is here, "to be made a fool" and "to be insipid." The choice of this words makes Christ use of "salt" as a metaphor for wit fairly clear. Only in this passage is this Greek word ever translated as "to make tasteless." Chemically, salt cannot lose its saltiness in the same way that a witty person can lose their common sense.
The Greek words translated as "wherewith" could mean a range of things from simply "in what" or "with anything." Both words have a wide range of meanings.
The word translated as "salted" is another play on words, and, as usual, one that only works in Greek. The Greek verb means "to salt" as in salting food, but it is a homonym with another verb meaning "to gather together" and, in the future passive, as it is here, "to going to meet together."
The verb translated as "it is good" means "to be strong." The phrase is not from the verb "is" with the adjective "good." This verb means "to be strong in body", "to be powerful," or "to be worth." Christ uses it primarily to mean "strong in body."
The two Greek words translated as "for nothing" means literally "in nothing" as you put salt and wit into something. Both words in this phrase have a wide variety of meanings (see following). The phrase could just as easily mean "in no matter" or "in regards to no one."
The word translated as "for" it not the usual word translated as "for," but a word that primarily means "into," and which usually has the sense of "in." However, it is a different "in" that the word above in "in what." It can mean "for" when describing a purpose but has a number of other uses as well.
The word translated as "nothing" also means "no one" and can mean, by itself, "good for nothing." If this was used with a verb form of "to be," the "good for nothing" meaning would be the clear winner. Unfortunately, it is not.
Two Greek words are translated as "except." They mean "if not." The "not" is the negative of opinion, so the sense is, "not thought." This plays with the whole "wit" idea.
The word translated as "cast" has a number of meanings revolving around "throw" as we do in English with both "throw" and "toss" but some that we don't have, such as "to fall." The form is passive and in the form of an adjective modifying "salt."
Christ ends the verse explaining what happens to those who have become foolish. They are cast out and trampled down. This sense is even clearer in Greek where the verb translated as "trodden under foot" is a metaphor for being spurned or rejected.
Salt is a metaphor for wit and for money.
The word translated as "lost savor" means "play the fool."
The word translated as "shall be salted" also means "to be brought together."
The word "to be good" means "to be worth," which is a play on the meaning of salt as money.
The use of the "salt" and "trodden upon" metaphors and a play on the two different meanings of the word translated as "to be salted."
The Spoken Version:
“You all are,” he continued affectionately, “the salt of the earth!” He tapped his temple knowingly to make it clear he was referring to the salt of their common sense. “But—” he said, striking his forehead with his palm as if something suddenly occurred to him. “What if?” He asked, “The salt is insipid? Played for a fool?”
The crowd laughed.
“In what,” the speaker demanded, “is it going to get salty?” He tapped his forehead again. “In nothing,” he said sadly. “It is worth nothing except being dumped out.” He made the motion of throwing out trash. “And being walked on by people.” He tramped around to illustrate.
Ὑμεῖς (pron 2nd pl nom) "Ye" is from humeis, which are the singular nominative form of the second person, "you." This version of hte pronoun is only used for emphasis.
τῆς γῆς: (noun sg fem gen) "Of the earth" is ge, which means "the element of earth", "land (country)", "arable land", "the ground," and "the world" as the opposite of the sky. Like our English word "earth," it means both dirt and the planet.
ἐὰν (conj) "If" is from ean, which is a conditional particle (derived from ei (if)and an (might)) which makes reference to a time and experience in the future that introduces but does not determine an event.
δὲ (partic) "But" is from de which means "but" and "on the other hand." It is the particle that joins sentences in an adversarial way but can also be a weak connective ("and") and explanation of cause ("so") and a condition ("if").
μωρανθῇ, (aor, pass, subj) "Lost his savour" is from moraino, which means "to play a fool", "to act foolishly", "to be silly," and "to be insipid."
τίνι (irreg sg dat) "Wherewith" is from tis (with en above) which can mean "someone", "any one", "everyone", "they [indefinite]", "many a one", "whoever", "anyone", "anything", "some sort", "some sort of", "each", "any", "the individual", "such," and so on. In a question, it can mean "who", "why," or "what."
λισθήσεται; (3rd sg fut ind pass) "Salted" is from halizo, which has two separate meanings, "to salt," as in salting food, and "to gather together," "to collect [pieces]," and "to meet together (passive)." The passive form of the "salted" form only typically applies to sheep, that is, putting out salt for them.
εἰς (prep) "For" is from eis, which means "into (of place)," "up to (of time)", "until (of time)", "as much as (of measure or limit)", "as far as (of measure or limit)", "towards (to express relation)", "in regard to (to express relation)", "of an end or limit," and "for (of purpose or object)."
ἔτι (adv) "It is thenceforth" is from eti, which means "yet" and "still" (with the Present), "already" (with the Past), "yet" and "longer" (with the Future), "no longer" (with a negative), and"still" and "besides" (of degree).
εἰ (conj) μὴ (conj) "But" is from ei me, which is the conjunction that means "if not", "but," and "except." εἰ is the particle use with the imperative usually to express conditions "if" or indirect questions, "whether." mê (me) is the negative used in prohibitions and expressions of doubt meaning "not" and "no."
βληθὲν (3rd pl aor ind pass or part sg aor pass neut nom) "Cast" is from ballo, which means "to throw", "to let fall", "to put", "to pour," or "to cast." "Cast" is from ballo, which means "to throw", "to let fall", "to put", "to pour," or "to cast."
καταπατεῖσθαι (pres inf mp) "To be trodden underfoot" is from katapateo, which means "to trod underfoot", "trample," and "trample down." It's literal meaning is "to walk down." It is also a metaphor for treating someone rudely or spurning them, treating them with neglect.