When Jesus said this, he provided men with an expression which has become the greatest compliment that can be paid to any man. When we wish to stress someone’s solid worth and usefulness, we say of him, “People like that are the salt of the earth.”

In the ancient world salt was highly valued. The Greeks called salt divine (theion, <G2303>). In a phrase, which in Latin is a kind of jingle, the Romans said, “There is nothing more useful than sun and salt.” (Nil utilius sole et sale.) In the time of Jesus salt was connected in people’s minds with three special qualities.

(i) Salt was connected with purity. No doubt its glistening whiteness made the connection easy. The Romans said that salt was the purest of all things, because it came from the purest of all things, the sun and the sea. Salt was indeed the most primitive of all offerings to the gods, and to the end of the day the Jewish sacrifices were offered with salt. So then, if the Christian is to be the salt of the earth he must be an example of purity.

One of the characteristics of the world in which we live is the lowering of standards. Standards of honesty, standards of diligence in work, standards of conscientiousness, moral standards, all tend to be lowered. The Christian must be the person who holds aloft the standard of absolute purity in speech, in conduct, and even in thought. A certain writer dedicated a book to J. Y. Simpson “who makes the best seem easily credible.” No Christian can depart from the standards of strict honesty. No Christian can think lightly of the lowering of moral standards in a world where the streets of every great city provide their deliberate enticements to sin. No Christian can allow himself the tarnished and suggestive jests which are so often part of social conversation. The Christian cannot withdraw from the world, but he must, as James said, keep himself “unstained from the world” (Jas 1:27).

(ii) In the ancient world salt was the commonest of all preservatives. It was used to keep things from going bad, and to hold putrefaction at bay. Plutarch has a strange way of putting that. He says that meat is a dead body and part of a dead body, and will, if left to itself, go bad; but salt preserves it and keeps it fresh, and is therefore like a new soul inserted into a dead body.

So then salt preserves from corruption. If the Christian is to be the salt of the earth, he must have a certain antiseptic influence on life.

We all know that there are certain people in whose company it is easy to be good; and that also there are certain people in whose company it is easy for standards to be relaxed. There are certain people in whose presence a soiled story would be readily told, and there are other people to whom no one would dream of telling such a tale. The Christian must be the cleansing antiseptic in any society in which he happens to be; he must be the person who by his presence defeats corruption and makes it easier for others to be good.

(iii) But the greatest and the most obvious quality of salt is that salt lends flavour to things. Food without salt is a sadly insipid and even a sickening thing. Christianity is to life what salt is to food. Christianity lends flavour to life.

The tragedy is that so often people have connected Christianity with precisely the opposite. They have connected Christianity with that which takes the flavour out of life. Swinburne had it:

“Thou hast conquered, O pale Galilaean; the world has grown
gray from Thy breath.”

Even after Constantine had made Christianity the religion of the Roman Empire, there came to the throne another Emperor called Julian, who wished to put the clock back and to bring back the old gods. His complaint, as Ibsen puts it, was:

“Have you looked at these Christians closely? Hollow-eyed,
pale-cheeked, flat-breasted all; they brood their lives away,
unspurred by ambition: the sun shines for them, but they do not
see it: the earth offers them its fulness, but they desire it not;
all their desire is to renounce and to suffer that they may come
to die.”

As Julian saw it, Christianity took the vividness out of life.

Oliver Wendell Holmes once said, “I might have entered the ministry if certain clergymen I knew had not looked and acted so much like undertakers.” Robert Louis Stevenson once entered in his diary, as if he was recording an extraordinary phenomenon, “I have been to Church to-day, and am not depressed.”

Men need to discover the lost radiance of the Christian faith. In a worried world, the Christian should be the only man who remains serene. In a depressed world, the Christian should be the only man who remains full of the joy of life. There should be a sheer sparkle about the Christian but too often he dresses like a mourner at a funeral, and talks like a specter at a feast. Wherever he is, if he is to be the salt of the earth, the Christian must be the diffuser of joy.

Jesus went on to say that, if the salt had become insipid, it was fit only to be thrown out and trodden on by men. This is difficult, because salt does no lose its flavour and its saltness. E. F. F. Bishop in his book Jesus of Palestine cites a very likely explanation given by Miss F. E. Newton. In Palestine the ordinary oven is out of doors and is built of stone on a base of tiles. In such ovens “in order to retain the heat a thick bed of salt is laid under the tiled floor. After a certain length of time the salt perishes. The tiles are taken up, the salt removed and thrown on the road outside the door of the oven … It has lost its power to heat the tiles and it is thrown out.” That may well be the picture here.

But the essential point remains whatever the picture, and it is a point which the New Testament makes and remakes again and again–uselessness invites disaster. If a Christian is not fulfilling his purpose as a Christian, then he is on the way to disaster. We are meant to be the salt of the earth, and if we do not bring to life the purity, the antiseptic power, the radiance that we ought, then we invite disaster.

It remains to be noted that sometimes the early Church made a very strange use of this text. In the synagogue, among the Jews, there was a custom that, if a Jew became an apostate and then returned to the faith, before he was received back into the synagogue, he must in penitence lie across the door of the synagogue and invite people to trample upon him as they entered. In certain places the Christian Church took over that custom, and a Christian who had been ejected by discipline from the Church, was compelled, before he was received back, to lie at the door of the Church and to invite people as they entered, “Trample upon me who am the salt which has lost its savour.” Barclay’s Daily Study Bible (NT).