Salt is mentioned in reference to covenants twice in the Old Testament, first here:
13 And every oblation of thy meat offering shalt thou season with salt; neither shalt thou suffer the salt of the covenant of thy God to be lacking from thy meat offering: with all thine offerings thou shalt offer . (Leviticus 2)
Then again here:
19 All the heave offerings of the holy things, which the children of Israel offer unto the Lord, have I given thee, and thy sons and thy daughters with thee, by a statute for ever: it is a of for ever before the Lord unto thee and to thy seed with thee. (Numbers 18)
Like so many other covenant symbols, salt has both positive and negative connotations. On the one hand, salt is an important preservative. On the other, in excess it can bring agricultural barrenness and desolation. Leviticus 2 contains some interesting concepts which will be the subject of this post:
Because salt was employed as a preservative, its use in a covenantal context also emphasized the expectation that the covenant would last for a long time... Because salt inhibits the leavening action of yeast, which represented rebellion, salt could additionally stand for that which prevented rebellion. An additional explanation for the appropriateness of salt in connection with the covenant is found in its association with agricultural infertility: In a Hittite treaty, the testator pronounces a curse: if the treaty is broken, “may he and his family and his lands, like salt that has no seed, likewise have no progeny.” (Zondervan,. NRSV, Cultural Backgrounds Study Bible, p. 832).
This adds context to Christ's famous saying:
13 Verily, verily, I say unto you, I give unto you to be the of the earth; but if the salt shall lose its savor wherewith shall the earth be salted? The salt shall be thenceforth good for nothing, but to be cast out and to be trodden under foot of men. (3 Nephi 12; see also Matthew 5)
23 ¶ And Abraham drew near, and said, Wilt thou also the with the ?
24 Peradventure there be fifty righteous within the city: wilt thou also destroy and not the place for the fifty righteous that are therein?
25 That be far from thee to do after this manner, to slay the righteous with the wicked: and that the righteous should be as the wicked, that be far from thee: Shall not the of all the earth do right?
26 And the Lord said, If I find in Sodom fifty within the city, then I will spare all the place for their sakes.
27 And Abraham answered and said, Behold now, I have taken upon me to speak unto the Lord, which am but and ashes:
28 Peradventure there shall lack five of the fifty righteous: wilt thou destroy all the city for lack of five? And he said, If I find there forty and five, I will not destroy it.
29 And he spake unto him yet again, and said, Peradventure there shall be forty found there. And he said, I will not do it for forty’s sake.
30 And he said unto him, Oh let not the Lord be angry, and I will speak: Peradventure there shall thirty be found there. And he said, I will not do it, if I find thirty there.
31 And he said, Behold now, I have taken upon me to speak unto the Lord: Peradventure there shall be twenty found there. And he said, I will not destroy it for twenty’s sake.
32 And he said, Oh let not the Lord be , and I will speak yet but this once: Peradventure ten shall be found there. And he said, I will destroy it for ten’s sake. (Genesis 18)
Ten righteous people can save an entire city from destruction. The principle here is that the righteous can serve as salt -- a preservative.
This also serves to highlight the significance of covenant rebellion. When none are found to be righteous, the people are in a truly terrible position. Paul gives us a somber summary of this state by pulling together verses from Psalms, Ecclesiastes, and Isaiah:
10 As it is written, There is , no, not one:
11 There is none that understandeth, there is none that seeketh after God.
12 They are all gone out of the , they are together become ; there is none that doeth , no, not one.
13 Their is an open sepulchre; with their tongues they have used deceit; the of asps is under their lips:
14 Whose mouth is full of cursing and :
15 Their feet are swift to blood:
16 Destruction and are in their ways:
17 And the way of have they not known:
18 There is no of God before their eyes. (Romans 3)
The highlighted passage above paraphrases Ecclesiastes 7:20.
The Book of Mormon makes use of this phrase twice to underscore the degree of wickedness preceding eras of destruction among the Nephites. The first example is here:
11 And because they did cast them all out, that there were none righteous among them, I did send down and destroy them, that their wickedness and abominations might be hid from before my , that the blood of the prophets and the saints whom I sent among them might not cry unto me the ground against them. (3 Nephi 9)
The other example is found at the end of the period of righteousness following the visitation of Christ:
46 And it came to pass that the robbers of did spread over all the face of the land; and there were none that were righteous save it were the disciples of Jesus. And gold and silver did they lay up in store in abundance, and did in all manner of traffic. (4 Nephi 1)
(Side note: "no, not one" from Romans 3:10 is also found twice in the Book of Mormon, both times in an interesting but unrelated context to the purpose of this post. See Moroni 7:17 and Moroni 10:25.)
The fancy word for this dual meaning is "bivalence" -- the covenant of salt highlights the fact that the same covenant which can bring about everlasting life also leads to severe consequences if rebellion sets in.