What does Matthew 5:13 mean?

Matthew 5:13 KJV
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.

Matthew 5:13 NKJV
“You are the salt of the earth; but if the salt loses its flavor, how shall it be seasoned? It is then good for nothing but to be thrown out and trampled underfoot by men.

Matthew 5:13 MKJV
You are the salt of the earth, but if the salt loses its savor, with what shall it be salted? It is no longer good for anything, but to be thrown out and to be trodden underfoot by men.

Matthew 5:13 KJV 2000
You are the salt of the earth: but if the salt has lost its savor, how shall it be salted? it is thereafter good for nothing, but to be cast out, and to be trodden under foot of men.

Interlinear KJV

Ye /humeis/ are /este/ the salt /halas/ of the earth: /ge/ but /de/ if /ean/ the salt /halas/ have lost his savour, /moraino/ wherewith /en/ /tis/ shall it be salted /halizo/? it is thenceforth /eti/ good /ischuo/ for /eis/ nothing, /oudeis/ but /ei me/ to be cast /ballo/ out, /exo/ and /kai/ to be trodden under foot /katapateo/ of /hupo/ men. /anthropos/

Albert Barnes’ Commentary

Verse 13. Ye are the salt of the earth. Salt renders food pleasant and palatable, and preserves from putrefaction. So Christians, by their lives and instructions, are to keep the world from entire moral corruption. By bringing down, by their prayers, the blessing of God, and by their influence and example, they save the world from universal vice and crime.

Salt have lost his savour. That is, if it has become insipid, tasteless, or have lost its preserving properties. The salt used in this country is a chemical compound—muriate of soda— and if the saltness were lost, or it were to lose its savour, there would be nothing remaining. It enters into the very nature of the substance. In eastern countries, however, the salt used was impure, mingled with vegetable and earthy substances; so that it might lose the whole of its saltness, and a considerable quantity of earthy matter remain. This was good for nothing, except that it was used, as it is said, to place in paths, or walks, as we use gravel. This kind of salt is common still in that country. It is found in the earth in veins or layers, and when exposed to the sun and rain, loses its saltness entirely.

Maundrell says,

“I broke a piece of it, of which that part that was exposed to the rain, sun, and air, though it had the sparks and particles of salt, yet it had perfectly lost its savour. The inner part, which was connected to the rock, retained its savour, as I found by proof.”

{h} “salt of the earth” Mr 9:50