In order to understand the Body of Christ's relationship to the New Covenant promises to Israel it is necessary to understand the meaning of the Greek word diatheke which is translated "covenant" in the following verse:
"For finding fault with them, he saith, Behold, the days come, saith the Lord, when I will make a new covenant (diatheke) with the house of Israel and with the house of Judah" (Heb.8:8; KJV).
Now let us look at this verse where the word diatheke is used as a promise which God made to Abraham:
"That we should be saved from our enemies, and from the hand of all that hate us; To perform the mercy promised to our fathers, and to remember his holy covenant (diatheke); The oath which he sware to our father Abraham" (Lk.1:71-73).
Geerhardus Vos wrote "in the Gospel i. 72 the 'diatheke' is equivalent to the promise given to the fathers; the parallelism in which it stands with the 'oath' of God proves this: 'to remember his holy 'diatheke,' the oath which He swore unto Abraham, our father'" [emphasis added] (Geerhardus Vos, "Hebrews, the Epistle of the Diatheke," The Princeton Theological Review, Vol. 13, No.4, 1915, 613 ).
Therefore, we can understand that the Greek word diatheke can mean a "promise."
In the first century no one would have understood the word diatheke to mean "covenant."
Adolf Deissmann wrote that "There is ample material to back me in the statement that no one in the Mediterranean world in the first century A.D. would have thought of finding in the word 'diatheke' the idea of covenant. St. Paul would not, and in fact did not. To St. Paul the word meant what it meant in the Greek Old Testament, 'unilateral enactment,' in particular a 'will or testament' " (Adolf Deissmann, Light From the Ancient East, translated by Lionel R.M. Strachan [London: Hodder and Stoughton, 1927], 337-338).
Next, let us look at the following translation of Jeremiah 31:31 to see that the the Hebrew word translated "covenant" at Jeremiah 31:31 is berith:
"Behold, the days come, saith the LORD, that I will make a new covenant (berith) with the house of Israel, and with the house of Judah" (Jer.31:31).
Louis Berkhof wrote that "In the Septuagint the word 'berith' is rendered 'diatheke' in every passage where it occurs with the exception of Deut. 9:15 ('marturion') and I Kings 11:11 ('entole'). The word 'diatheke' is confined to this usage, except in four passages. This use of the word seems rather peculiar in view of the fact that it is not the usual Greek word for covenant, but really denotes a disposition, and consequently also a testament. The ordinary word for covenant is 'suntheke'" [emphasis added] (Louis Berkhof, Systematic Theology [Grand Rapids, 1949], 262-263).
According to Berkhof the Greek word diatheke denotes a "disposition" as well as a "testament." In the The Vocabulary of the Greek Testament we read that the word diatheke "is properly 'dispositio,' an 'arrangement' made by one party with plenary power, which the other party may accept or reject, but cannot alter" (J.H. Molton and G. Milligan, The Vocabulary of the Greek Testament [Grand Rapids: Eerdmans, 1930], 148).
Here we see that the translators of the Greek Old Testament (LXX) used the Greek word diatheke to translate the Hebrew word berith:
"Behold, the days come, saith the LORD, that I will make a new covenant (diatheke) with the house of Israel, and with the house of Judah" (Jer.31:31; LXX).
Vos also wrote that the Greek word diatheke can mean "disposition," writing that "all that they (the translators of the Greek New Testament) wanted out of 'diatheke' was the emphasis which the word enabled them to throw upon the one-sided initiative and the unimpaired sovereignty of God in originating the order of redemption...Their procedure appears intelligent only on the supposition that they believed 'diatheke' capable of retaining or reacquiring the sense of 'disposition'" [emphasis mine] (Geerhardus Vos, "Hebrews, the Epistle of the Diatheke," 604-605 ).
Now let us look at the following verse:
"That at that time ye were without Christ, being aliens from the commonwealth of Israel, and strangers from the covenants (diatheke) of promise, having no hope, and without God in the world" (Eph.2:12).
In his commentary on this verse Vos says that "in Eph. ii. 12 the phrase 'covenants of the promise,' in which the genitive is epexegetical, yields positive proof that Paul regards the 'diatheke' as so many successive promissory dispositions of God, not as a series of mutual agreements between God and the people" [emphasis added] (Ibid., p.609).
The word diatheke does not carry with it the sense of a compact or of a mutual agreement between two parties, which is the normal understanding of a covenant. Albert Barnes wrote that "the writers of the New Testament never meant to represent the transactions between God and man as a 'compact or covenant' properly so called. They have studiously avoided it...The word which they employ - 'diatheke' - never means a compact or agreement as between equals" (Barnes' Notes on the Bible, Commentary at Hebrews 8:8).
Even though Robert Saucy is a Progressive Dispensationalist he recognizes that the New Diatheke is essentially a "promise," writing that "because of its gracious promissory nature, the new covenant is frequently identified with the covenants of promise" [emphasis added] (Saucy, The Case for Progressive Dispensationalism [Grand Rapids: Zondervan Publishing House, 1993], p.121).
J. H. Moulton and G. Milligan say that diatheke "is properly 'dispositio,' an 'arrangement' made by one party with plenary power, which the other party may accept or reject, but cannot alter. A 'will' is simply the most conspicuous example of such an instrument, which ultimately monopolized the word just because it suited its differentia so completely" [emphasis added] (J.H. Molton and G. Milligan, The Vocabulary of the Greek Testament [Grand Rapids: Eerdmans, 1930], 148).
So we can see that the Greek word diatheke can mean a "Promissory Disposition" and it can also mean a "Last will and Testament."
Next we will examine the following translation of 2 Corinthians 3:6 and we will see that "new testament' is the correct translation:
"Who also hath made us able ministers of the new testament; not of the letter, but of the spirit: for the letter killeth, but the spirit giveth life" (2 Cor.3:6; KJV).