Matthew 5:13 in detail,  salt losing its saltiness

1. Parallel passages

Luke 14:34-35

“34Salt is good, but if the salt becomes flat and tasteless, with what do you season it? 35It is fit neither for the soil nor for the manure pile. It is thrown out. He who has ears to hear, let him hear.”

(Luke 14:34-35 WEB)

In Luke, Jesus’ parable of the banquet (Luke 14:7-24) sets the scene for this parallel. As multitudes continue to follow him (Luke 14:25), Jesus clarifies that there would be a cost, and it might involve renouncing family or even their own life (Luke 14:26, 28, cf. Exod 32:29). If a king with only a small army cannot overthrow a large one, i.e. God is not with him (cf. Lev 26:8, Deut 32:30), then it better to seek peace terms than confrontation (Luke 14:31-32). Whoever does not renounce all, cannot be Jesus’ disciple (Luke 14:33). Tasteless salt is fit only to be thrown out.

Mark 9:49-50

9:49 “For everyone will be salted with fire, and every sacrifice will be seasoned with salt.9:50 Salt is good, but if the salt has lost its saltiness, with what will you season it? Have salt in yourselves, and be at peace with one another.”

(Mark 9:49, WEB)

This passage, which again has apocalyptic overtones, is dealt with elsewhere as part of a wider consideration of Mark 9: 36-50.

2. Potential uses of salt

To sustain life

Salt is lost through sweating and therefore a certain amount is required in the diet. Ancient communities in Palestine were well aware that salt was a necessity for life (Herr 2002, 286).

As a preservative

The volume of salt used for the preservation of foodstuff dwarfed that used for any other purpose. The availability of certain foods was often intermittent because of a restricted harvest season, climatic uncertainty or the migratory behaviour of mammals, birds or fish. Under such circumstances a community that could store food would fare better than one that could not. Salting was one of the relatively few reliable techniques for long term storage of perishable foodstuffs and it used significant amounts of salt. Dessication was another method, though, where meat was involved, it too usually required the use of salt (e.g. see Stott, 2003, 58). In Galilee, fish was routinely preserved by salting (Negev 1996a, n.p.), e.g. on its shore lay Migdal Nunayah (‘tower of fishermen’), aka Tricheae(‘drying and salting’). Furthermore, Jesus had just come from the lakeside city of Capernaum, bringing some of its fishermen along as disciples (Matt 4:18-22). It is therefore easy to see in Matt 5:13, the suggestion that Jesus’ disciples were supposed to preserve the world from corruption (e.g. see Bullinger 1898, 738).

Leather was originally preserved by tanning it with salt alone, though salt is now used in combination with other chemicals (Negev 1996b, n.p.). To render a raw hide supple it was throwing out into the street to be trampled under foot, a practice which may have informed Jesus’ choice of words in Matt 5:13. It was then beaten and rubbed with dog’s dung, before thorough washing and drying (Negev 1996b, n.p.).

Parchment was produced from hides by salting them and then treating them with flour (Negev 1996b, n.p.). Such parchment would have been reserved for the more important documents, such as legal agreements.

As a commodity

Salt was a valuable commodity in antiquity (Negev 1996a, n.p.) and the international trade in it could make or break fortunes (Bloch 2008, n.p.). In the Eastern Mediterranean region, refined salt has been produced by evaporation for millennia (Bloch 2008, n.p.). The technique uses salt pans, within which salty water is concentrated until pure salt (halite) begins to crystallise out. The unique properties of Sodium Chloride then mean that halite crystallises onto floating objects whilst the other salts crystallise on the bottom of the brine, thus enabling salt makers to refine the salt using low-tech floating wooden frames. The first Century Palestinians, probably practiced such evaporation techniques around the Dead Sea, for there are traces of ancient salt pans in the area and it is notable that Ezekiel’s prophecy of the freshening of the Dead Sea leaves the valuable salt marshes unaltered (Ryken et al 2000a, 557; Ryken et al 2000b, 752). Furthermore, Zephaniah mentions salt pits (Zeph 2:9) which may well have been in this area.

In addition to the Dead Sea sources, those in Palestine also had easy access to relatively pure salt from Jebel Usdum (Mt Sodom), a four-mile-long ridge of rock salt (Negev 1996a, n.p.). This geological structure, known as a salt diapir, contains vast quantities of 99% pure crystalline halite (Vil’bushevich 1920, 10).

Bloch suggests that, salt production from coastal salt pans was very vulnerable to flooding due to sea level fluctuations, unlike inland salt production (Bloch 2008, n.p.). Furthermore, he speculates that Herod the Great’s rise to power was at least in part funded by his ability to cash in on a temporary glitch in coastal salt production.

As a flavouring

Salt was used on food because of its well known taste enhancing properties, these are referred to in Job 6:6 (Negev 1996a, n.p.).

For its medicinal properties.

Usually suggested because of salt’s mild antiseptic qualities and the Arab practice of rubbing newborn babies with salt (Negev 1996a, n.p.). The baby rubbing practice is referred to in Ezek 16:4. However, I have been unable to find any primary evidence that this was for clinical reasons.

As a fertilizer

Newton states that “common salt, or sodium chloride, has been used for many years in the older countries. It supplies no essential ingredient of plant-growth. The value as a fertilizer is probably due to its action in the soil of setting free more important elements” (2009, 15). Its effects on growth are seldom particularly striking, however its use improves the hardiness and disease resistance of a variety of crops, it also makes pasture more attractive to livestock (Sprengle 1845, 180). The salt may be sprinkled directly on the land or applied to the dung-heap before that is spread (Sprengle 1845, 181), a practice apparently alluded to in Luke 14:34-35 (Sprengle 1845, 181). Direct application is likely to be less effective on the limestone hills of Israel, as the salt reacts chemically with chalky soils (Sprengle 1845, 180). However, humic acid, released from the decay of organic matter, is known to reverse this reaction (Sprengle 1845, 180).

As a soil fertility inhibitor

Whilst small quantities of common salt can act as a fertilizer, in larger quantities it destroys soil fertility. Abimelech is said to have sowed a city with salt (Judg 9:45), though this may be no more than a symbolic act to indicate that it was suffering the fate of Sodom (Deut 29:23). Another reference to this practice is possibly to be found in Jeremiah’s prophecy concerning Moab (Jer 48:9 NIV, cf. Jer 48:9 NKJV, Zeph 2:9). Outside the biblical context, it is possible that such a practice is alluded to in a Greek myth in which Odysseus feigns madness by ploughing with mismatched animals (a donkey and an ox, cf. Deut 22:10) and sowing salt (Frazer n.d., n.p.).

To increase the brilliance of a lamp

One technique for producing a brighter flame on a traditional oil lamp was to add salt to the wick (Elwell and Comfort 2001, 797). This clearly of interest given the content of Matt 5:14-16.

3. Can salt loose its saltiness?

Sodium chloride (NaCl) is a relatively inert chemical, so it remains immune to normal environmental processes except for solution and retains its characteristic taste. Scholars have therefore attempted to understand Jesus’ logic behind suggesting that salt could loose its saltiness. Some consider that because such a change cannot happen, Jesus is using this to emphasise the impossibility of his disciples loosing their ‘saltiness’ (as noted by Bertram 1964, 838). Others have suggested that he was drawing an analogy with a way in which real salt, or a similar substance, could be thought to loose its saltiness (Bertram 1964, 838).

There are two widely mentioned theories for a type of saltiness-loosing salt that Jesus might have had in mind. The first proposes that Jesus’ was thinking of the sediments or evaporite deposits that, whilst colloquially called “salt”, contained substantial amounts of other materials, in contrast to the mineral halite or refined salt (e.g. see Bertram 1964, 838). The second proposal suggests that Jesus was alluding to the refined salt used in an Arab baking technique (e.g. see Bertram 1964, 838).

The Arab baking technique used salt blocks in the floor of the oven. These gradually lost their effectiveness and then had to be renewed (Bertram 1964, 838). This use of salt in ovens is probably related to its lack of pore space and high specific energy, which mean that it can be directly heated to very high temperatures without breaking (as a clay-based brick might). They also cause it to hold heat well, so it is less effected by opening and closing an oven door. However, there would seem little in this process, other than mechanical wear, that would change the chemical composition of the block and result in loss of saltiness. Moreover, Jesus usually drew his illustrations from the scriptures or common first-century Jewish experience. As the Sermon’s audience were not primarily Arab bakers, such an illustration might seem inappropriate.

The theory relating to impure salty material sounds rather more plausible, as salty sediments were available in Judea and could gradually loose their saltiness by leaching if left in the rain. However, there are difficulties with this hypothesis. In the first instance, in such a salt rich country people had little reason to use impure salt. It would be harder to transport (because of the additional bulk) and it would be less effective as a preservative (you would need more and it’s impurities would contaminate the food). Secondly, it is often assumed that such impure salt was readily obtained from the Dead Sea, which is in practice far from the case.

The Dead Sea has been an enduring haline lake for millennia (Frumkin & Elitzur 2002, 334), however it has an unusual water composition and a tendency to stratification. This results in surface waters in which sodium chloride (NaCl) is not the major component (Stienhorn 1983, 581). Common salt (NaCl) comprises about 30% of the salt, with magnesium chloride (MgCl2), calcium chloride (CaCl2) and potassium chloride accounting for the majority of the remainder. Na, Mg, Ca and K occur in the rough proportions 39:45:17:8 (Niemi, Ben-Avraham and Gat 1997, 162). The remainder, which comprises less than 1%, is mostly carbonates, bromides and sulphates. Thus, as both magnesium and potassium chlorides are bitter, such Dead Sea salt, at least in its unrefined form, is unsuitable for use in preserving food. Furthermore, magnesium chloride is substantially more soluble in water than sodium chloride (Floor 2006, n.p.). Thus, if impure Dead Sea salt were exposed to damp conditions, one would envisage them getting saltier as the rapid leaching of magnesium chloride left a residue containing a higher proportion of sodium chloride. Leave them in the rain long enough for the halite component to dissolve and there would be nothing worth throwing out left, for all the Dead Sea salts, except the really minor constituents, are readily soluble in water (Dawson 1892, 109).

Salt from Jebel Usdum, like most rock salt, contained traces of insoluble residue (Vil’bushevich 1920, 10). The hill is also capped with deposits of gypsum and shale that falls onto the salt below (Hull 1885, 129-132). Thus, salt from this source could dissolve to leave a lumpy or dusty residue. However, it is debatable why anyone would use such tainted salt, when far purer salt was available at the same site for a trivial amount of digging or by refinement from the nearby Dead Sea. As ancient cultures were adept at producing pure salt from saline brines, the commercially available product was unlikely to have left much noticeable residue when exposed to rain.

The prevalence of a trade in salt suggests a further way in which salt could loose its saltiness. Unscrupulous traders could pass-off as salt an admixture with some other cheap and tasteless mineral (such as Gypsum, which was also abundant in the area (Vilbushevich 1920, 10)) that, when ground up, nevertheless resembled salt. Salt would then loose its saltiness because somebody was actively introducing a worthless foreign substance, which whilst looking like the real thing, was effectively useless.

4. The salt of the world

“You”, said Jesus of his disciples, “are the salt of the world” (Matt 5:13 WEB). The Greek gives us few clues as to the intended scope of “world,” for the Greek word γῆ (ge) is far from precise. It can refer to the ground (i.e. the soil and rock), a land (e.g Egypt or Israel) or the entire planet, depending upon its context. Historically, it has usually been taken to be global, but it is perhaps more accurate to think of the land as being wherever the children of the covenant set their feet.

The parallel version of this passage, in Luke 14:35, states explicitly the sort of use for which the salt was no longer fit. It was no longer valuable for use on the dunghill or on the land (γῆ). This would seem to imply an agricultural metaphor, i.e. use as fertilizer, in which case γῆ would equate to the soil or agricultural land. It might equally express two opposite uses of salt, via the dunghill as a fertilizer and directly to the land as a growth inhibitor.

5. Jesus’ disciples as preservative

Many expositors draw the link between salt’s preservative properties and a disciples role in the entire world (e.g. Stott, 2003, 59-60, Lloyd-Jones, 1962, 151-152). However, there was perhaps a more specific preservative role that Jesus was referring to. The Bible identifies two of the divine covenants as covenants of salt. Those in question are:

Neither passage identifies precisely what a covenant of salt was. However, it is notable that on both occasions a human authority was being entrusted with bringing wise and Godly judgements. As the Sermon on the Mount addresses the legal foundation of a covenant. It is therefore tempting to see a link between the salt of the covenant and the salt of the world.

The link between salt’s preservative properties and the enduring nature of key biblical covenants is often noted (e.g. Negev 1996a, n.p.). Just as it allowed other things to be kept from deteriorating, so the ‘salt’ would keep the covenant relationship from deteriorating. In eastern culture, there being ‘salt between us’ was an expression that a good relationship existed. Eating salt together was therefore a symbol of the good relationship that kept a covenant beneficial. According to Leviticus, the ‘salt of the covenant’ was to be on every offering, or possibly every grain offering (Lev 2:13), a handful of which went to the Lord and the remainder was eaten by the priests. This amounted to taking salt on a meal shared with God and may have been understood in a similar way (e.g. Negev 1996, n.p.)

6. Salt as a symbol of wisdom

R. T. France (France 1995, 112) notes that Jewish teachers often used salt as a symbol of wisdom and that the phrase “looses its saltiness” is a poor reflection of the Greek. He suggests that Jesus used an Aramaic word that means both “to loose flavour” and also “to become foolish”. The Greek word used here is the same one used in the LXX version of Jer 5:20-21, a passage that, like Luke 14:35, implies that the wise will have ears to hear. That passage states -

5:20 “Declare this in the house of Jacob, and publish it in Judah, saying,
5:21 ‘Hear now this, foolish people, and without understanding; who have eyes, and don’'t see; who have ears, and don’t hear.’”

(Jer 5:20-21 WEB)

The symbolic link between loosing saltiness and acting foolishly comes across particularly well in one of the teachings of Jesus Ben Sirach. In this wisdom saying he chooses to parallel a mouthful that lacks salt with the mouth of a fool -

20:19 “As the fat tail of a sheep, eaten without salt, So is a word spoken out of season.
20:20 A parable from the mouth of a fool is worthless, For he uttereth it out of season.”

(Sirach 20:19-20, Charles, R. H., Apocrypha of the Old Testament, 2002)

The fat tail from a sacrificial sheep was always offered to (i.e. consumed by) God and it was supposed to be offered with salt, it was therefore unwise to omit the salt. 

Paul seems to have recognised salt as a metaphor for wisdom when he advised the Colossians -

4:5 “Walk in wisdom toward those who are outside, redeeming the time.
4:6 Let your speech always be with grace, seasoned with salt, that you may know how you ought to answer each one.”

(Col 4:5-6 WEB)

Matthew 5:13 might therefore be paraphrased as ‘if your wisdom has become foolishness, then who will make you wise again’. Indeed Luz (2007 ,203), recognising this, offers “But when the salt becomes dumb.”

The clear parallel between “You are the salt of the earth” (Matt 5:13 WEB) and “you are the light of the world” (Matt 5:14 WEB) is particularly illuminating [pun intended], for the brilliance of light was (and is) another common biblical metaphor for wisdom (see commentary on Matt 5:14-16). Furthermore, as Proverbs amply demonstrates (Prov 2:1-10), wisdom is intimately linked to paying attention to your father’s commandments, the topic of Matt 5:17-20.

Recognising Jesus’ salt as a symbol of wisdom makes good sense of Mark’s Gospel’s “Have salt in yourselves,and be at peace with one another.” (Mark 9:50 WEB). That the embodiment of Godly wisdom led to peace, is a foundational tenant in Biblical books such as Proverbs. For example, see Pr 3:1-17, a passage that embodies the idea that embracing the Way of Righteousness leads to peace.

Taking salt as a metaphor for wisdom is also helpful in the case of Elisha’s miraculous healing of a spring, for it adds a significance to casting salt that is entirely in keeping with the role of a true prophet. Thus the situation at Jericho is presented as a metaphor for the role of the prophet within all Israel as we read -

19 ‘The men of the city said to Elisha, “Behold, please, the situation of this city is pleasant, as my lord sees; but the water is bad, and the land miscarries.” 20 He said, “Bring me a new jar, and put salt in it.” They brought it to him. 21 He went out to the spring of the waters, and threw salt into it, and said, “Thus says the LORD, ‘I have healed these waters. There shall not be from there any more death or miscarrying.’” 22 So the waters were healed to this day, according to the word of Elisha which he spoke.’

(2 Kgs 2:19-22 HNV)

7. How can it be made salty again?

Reference to salt being made salty again is found within the proverbs preserved in the Talmud (France 1995, 112) . It reports that Rabbi Joshua ben Hananiah, who died about 130 C.E., was posed a question by an enquirer, “When salt loses its flavour, how can it be made salty again?” (b. Bek. 8b). It would seem that the teaching of the Sermon on the Mount influenced the question, for the Rabbi’s reply, “By salting it with the afterbirth of a mule,” made it quite clear that he considered this impossible (as was getting an afterbirth from a sterile hybrid animal like a mule), whilst taking a mighty side-swipe at the earlier Christian’s claim to be the salt of the world (by inferring that they were the lifeless remnant of a fictitious miracle birth).

Jesus also seems to envisage that such recovery was impossible as he suggests such salt must be thrown out, and presumably replaced with fresh. As Jesus was not talking primarily about sodium chloride but about wisdom, there was an obvious source from which that replacement could come. God’s words were both pure wisdom and eternal.

8. Thrown out and trampled under foot

The association of salt with wisdom in the final words of Matt 5:13 is clarified by Mark’s Gospel. There we find a parallel phrase, “Salt is good, but if the salt has lost its saltiness, with what will you season it?” (Mark 9:50a WEB), which falls in the conclusion of an exchange between Jesus and his disciples. This discussion concerns the fate of those who abuse their authority and lead the trusting into idolatrous error (see notes on Mark 9:36-50). 

Jesus’ suggests that it is better for leaders to suffer the ultimate sanctions under the covenant of Moab (Deut 28:64-65), of captivity, servitude and exile, than continue to be allowed to lead the trusting astray.  When those entrusted with ensuring that the covenant was kept, i.e. Israel’s ‘salt’, stopped listening to God’s words, then they became foolish and the curses began to bite. It had happened in the Northern kingdom with the consequent destruction of the nation and exile of its people. It had then happened in Judah, with similar results. However, in Judah’s case, because of God’s faithfulness to the heirs of David, he preserved a remnant from that house, a pinch of salt that had not become foolish. 

The whole issue of salt loosing its saltiness was tied, through the covenant of Moab, to doing all the words of the law (Deut 29:9, 29). If the human salt entrusted with preserving the law lost their salty wisdom then there was no hope of achieving such full compliance. Thus, when God’s people turned their back on the law, they, along with their ineffective “salt”, risked being cast out to suffer a downtrodden existence among the nations. Little wonder then that fulfilling every last word of the law would, in a few verses, become the focus of the Sermon.  Tom Wright suggests that the Sermon on the mount was “a challenge to Israel to be Israel” (Wright 2001, 288), but I would suggest that in this passage we have a challenge to Israel’s spiritual leaders to ensure that Israel continues to be Israel.