In Numbers 18:19, God says the holy contributions made by the people of Israel belong to Aaron and his descendants forever, as a "covenant of salt". I've never seen this term before. What does it mean?
A covenant of salt in the Bible
The term covenant of salt is found three times in the Old Testament:
Leviticus 2:13 `And every offering of your grain offering you shall season with salt; you shall not allow the salt of the covenant of your God to be lacking from your grain offering. With all your offerings you shall offer salt.'[NKJV]
Notice here that the offerings were to be seasoned with salt, which is identified as the salt of the covenant.
Numbers 18:19 "All the heave offerings of the holy things, which the children of Israel offer to the LORD, I have given to you and your sons and daughters with you as an ordinance forever; it is a covenant of salt forever before the LORD with you and your descendants with you."[NKJV]
This verse is in reference to establishment of the Aaronic Priesthood.
2 Chronicles 13:5 "Should you not know that the LORD God of Israel gave the dominion over Israel to David forever, to him and his sons, by a covenant of salt?"
This verse is in reference to the establishment of Davidic dynasty.
What does it mean?
One commentator notes that the origin of the phraseology is unknown1, however many reliable sources believe the relevance lies in the functions of salt in a covenant meal.
For example we read:
Covenant of Salt.
Biblical phrase for a two-way agreement, the inviolability of which was symbolized by salt. A Middle Eastern saying, “There is bread and salt between us,” meant that a relationship had been confirmed by sharing a meal. Salt symbolized the life and enduring nature of the alliance. In the OT salt appears in the relationship between God and Israel (Lv 2:13). As a purifying agent and preservative in the cereal offering, salt symbolized the indissoluble nature of the covenant between God and Israel. [Elwell, W. A., & Beitzel, B. J. (1988). In Baker encyclopedia of the Bible (p. 538). Grand Rapids, MI: Baker Book House.]
Covenant of salt
As salt was regarded as a necessary ingredient of the daily food, and so of all sacrifices offered to Yahweh (Lev 2:13), it became an easy step to the very close connection between salt and covenant-making. When men ate together they became friends. Cf. the Arabic expressions, "There is salt between us"; "He has eaten of my salt," which means partaking of hospitality which cemented friendship; cf. "eat the salt of the palace" (Ezra 4:14). Covenants were generally confirmed by sacrificial meals and salt was always present. Since, too, salt is a preservative, it would easily become symbolic of an enduring covenant. So offerings to Yahweh were to be by a statute forever, "a covenant of salt for ever before the Lord" (Num 18:19). David received his kingdom for-ever from the Lord by a "covenant of salt" (2 Chron 13:5). In the light of these conceptions the remark of Our Lord becomes the more significant: "Have salt in yourselves, and be at peace with one another" [from International Standard Bible Encyclopedia, revised edition, Copyright © 1979 by Wm. B. Eerdmans Publishing Co.]
Others have suggested that:
The term "covenant of salt" is indicative of the everlasting nature of the relationship between the children of salt, and their Elohim Yahweh. When we hear the term salt, the understanding is that the things Yahweh addresses are eternal, enduring, never changing, and abiding forever. All salt covenants then are eternal, and eternally binding on the sons and daughters of Yisrael, regardless where they are to be found, and regardless of whether a physical temple stands on Mt. Moriyah or not.[source]
I am not convinced the term can be limited to that because:
1) The covenants that God makes with man are perpetual, see for example Gen 17:7, 2 Sam 23:5 so it seems redundant to use salt to specify the perpetual nature of the covenant.
2) The salt of the covenant was used to season all the sacrifices, many of which were eaten by the priests and those offering them. The priest ate of the grain offering, the peace offering, the sin offering and the trespass offering, and the peace offering was eaten by those offering it as well2.
The people participated in the sacrifices by the eating of them as well as the offering of them, and those sacrifices were seasoned with salt; hence I favour the emphasis provided by the Baker encyclopedia of the Bible and the Standard Bible Encyclopedia mentioned above, as one commentator notes, "It is a common phrase among Oriental people, who consider the eating of salt a pledge of fidelity, binding them in a covenant of friendship."3
The phrase doesn't just emphasis the perpetual nature of the covenant but also the friendly nature of it as well.
1 NAC. Cole, R. D. (2000). Numbers (Vol. 3B, p. 290). Nashville: Broadman & Holman Publishers.
2 Details of these offerings can be found in the following passages: :Burnt offering - Lev 1; 6:8-13; 8:18-21; 16:24 :Grain Offering - Lev 2; 6:14-23 :Peace Offering - Lev 3; 7:11-34 :Sin offering - Lev 4; 5:1-13; 6:24-30; 8:14-17; 16:3-22 :Trespass offering - Lev 5:14-19; 6:1-7; 7:1-6
3 Jamieson, R., Fausset, A. R., & Brown, D. (1997). Commentary Critical and Explanatory on the Whole Bible (Vol. 1, pp. 108–109). Oak Harbor, WA: Logos Research Systems, Inc.
I do believe there was a book written about this. The point isn't that the sacrifices were seasoned with salt but instead there was an exchange of salt. Or the way I see it is God provides the salt, from the earth, and we exchange it with Him in an offering.
Let's remember this was around 3,000 years ago. Salt was like gold, rare and only for the wealthy. Similarly, sugar was too.
For traders, salt was used to pay wages. Source: Salt: A World History by Kurlansky
From what I remember, salt was carried by many travelers. They each had a pouch containing salt. When two travelers came into agreement on something, they'd seal the agreement with an exchange of salt. I give you a pinch of mine, you give me a pinch of yours, and we both place that salt in our pouches. It implies that for either of us to break the agreement, we'd have to find the salt that we gave you, to take back our agreement. Or, in other words, it was a lasting agreement.
Leviticus 2:13 Season all your grain offerings with salt. Do not leave the salt of the covenant of your God out of your grain offerings; add salt to all your offerings.
I view this as God saying that He wanted us to exchange salt with us due to that cultural tradition. That God wanted to enter into a lasting agreement with us.
Salt is by nature a preservative and also a seasoning. A Covenant is an agreement between two or more parties. With God, it's a binding ensign between the Creator and His creatures, wherewith God binds Himself and expects the other parties to comply with His will to symbolise the oath.
In Leviticus 2:13 it refers to "seasoning", one of the functions of salt -- to season means to give it taste. The "preservative" function of salt is also applicable since it is added to food items used for sacrifices so that the object of sacrifice endures and doesn't go bad.
The "preservative" function of salt is the meaning intended by the statement of King Abijah in 2 Chronicles 13:5, that the kingdom handed to David is an enduring one, "preserved" for him by a covenant.
So it can be inferred that covenant of salt means a covenant that is alive (not spoiled) and enduring.
Edward Bagby Pollard puts it this way:
solt (berith melach; halas, classical Greek hals): As salt was regarded as a necessary ingredient of the daily food, and so of all sacrifices offered to Yahweh (Leviticus 2:13), it became an easy step to the very close connection between salt and covenant-making. When men ate together they became friends. Compare the Arabic expression, "There is salt between us"; "He has eaten of my salt," which means partaking of hospitality which cemented friendship; compare "eat the salt of the palace" (Ezra 4:14). Covenants were generally confirmed by sacrificial meals and salt was always present. Since, too, salt is a preservative, it would easily become symbolic of an enduring covenant. So offerings to Yahweh were to be by a statute forever, "a covenant of salt for ever before Yahweh" (Numbers 18:19). David received his kingdom forever from Yahweh by a "covenant of salt" (2 Chronicles 13:5). In the light of these conceptions the remark of our Lord becomes the more significant: "Have salt in yourselves, and be at peace one with another" (Mark 9:50). See http://biblehub.com/topical/c/covenant_of_salt.htm
So as others here have mentioned it is a symbol of
- Friendship and Peace
- An Enduring Covenant
But I'd also like to add that the New Testament adds a new perspective to the salt of the covenant. We know from Leviticus 2:13 that
And every offering of thy present shalt thou season with salt, and thou shalt never allow the salt of the covenant of thy God to be lacking from thy present; with all thine offerings thou shalt offer salt.
This concept of salt as an essential component of every offering is repeated in the New Testament too
Mark 9:49 says
For every one shall be salted with fire, and every sacrifice shall be salted with salt.
Now, in the context of the New Testament the great offering is Christ. 1 Cor 5:7 says:
Purge out therefore the old leaven, that ye may be a new lump, as ye are unleavened. For even Christ, our passover, is sacrificed for us;
And also Ephesians 5:2
and walk in charity even as the Christ also has loved us and has given himself for us as an offering and a sacrifice to God for a sweet smelling savour.
Now every sacrifice was to be offered with an additional element... salt, but where's the salt here? If Jesus is the offering, who or what is the salt? We are...
Matthew 5:13 says
Ye are the salt of the earth, but if the salt has lost its savour, with what shall it be salted? From then on it is good for nothing, but to be cast out and to be trodden under foot of men.
So here we find that in order for the sacrifice of Christ to be effective in the lives of Jesus's followers, they must be part of the sacrifice as well, they must offer themselves as part of the sacrifice. This idea is reinforced in Romans 12:1
Therefore, I beseech you brethren, by the mercies of God, that ye present your bodies in living sacrifice, holy, well pleasing unto God, which is your rational worship.
Another verse related to Jesus' followers being the salt is Luke 14:34. The context of this verse is the requirements for being Christ's disciples. We read in Luke 14:27,33-35
And whosoever does not bear his cross and come after me cannot be my disciple. [...] So likewise, any one of you that does not forsake all that he has cannot be my disciple. Salt is good; but if the salt has lost its savour, with what shall it be seasoned? It is neither good for the land, nor for the dunghill; it is cast out. He that has ears to hear, let him hear.
Once again we see the idea of a daily sacrifice of the self in being a follower of Jesus.
In summary... In the Old Testament salt was a symbol of friendship and peace and also of an enduring covenant between two persons or groups. In the New Testament it keeps and reinforces these meanings, but also reminded his followers that they must take part in Jesus' sacrifice by "offering [themselves] as living sacrifices" to God.
Actually, the salt covenants are in the texts quoted by the OP and there were two such:
- The Levitical Covenant of Salt (Lev 1-9, 16, 21-27, Num 3, 4, 8, 18, 25:10-13, Deut 33:8-11, Neh 13:29, Mal 2:4-8. This is an eternal covenant (Num 25:12, 13, Ps 106:30, Jer 33:18, 21, 22) of salt, Num 18:19.) It is a covenant between God and the tribe of Israel. The salt element was added (Num 18:19) as a symbol of its solemnity. As a memorial of this, as part of the old ceremonial system, salt was added to all offerings:
Lev 2:13 - You shall season all your grain offerings with salt. You shall not let the salt of the covenant with your God be missing from your grain offering; with all your offerings you shall offer salt.
Eze 43:24 - You shall present them before the LORD, and the priests shall sprinkle salt on them and offer them up as a burnt offering to the LORD.
- The Davidic or Royal Covenant of Salt (2 Sam 7, 23:5, 1 Kings 6:11, 12, 8:25, 1 Chron 17:11-14, 2 Chron 6:14-16, 7:17, 18, 13:5, Ps 89:4, 29, 34, 39, 132:11, 12, Jer 33:17, 21, Eze 37:15-28. This is an eternal covenant; 2 Sam 23:5, 1 Kings 9:5, 2 Chron 13:5, Eze 37:25, 26, Jer 33:17, 21 or salt, 2 Chron 13:5.) It a covenant between God and the royal line of David through whom the (humanly speaking) the Messiah would be born. The salt element was added (2 Chron 13:5) as a symbol of its solemnity.
Thus, there are no records of any private covenants between people involving salt - the only covenants of salt are divine covenants between God's people and God, initiated by God.