διαθήκη

There is a Greek word at the center of how Christians describe their Bible. We call the two main divisions of the Bible the Old Testament and the New Testament. The Greek word behind both names is diathēkē.

Most Christians have used this language their entire lives without thinking about what it means. The “Old Testament” is not just “the older books.” It is the older testament. The “New Testament” is not just “the more recent books.” It is the newer testament. And the question of what a testament is — and what makes one new — is what this chapter is about.

It is also the word Jesus used the night before He died, when He took the cup at the Last Supper and said: “This is my blood of the covenant” (Matt 26:28). Or, as Paul preserves the saying: “This cup is the new covenant in my blood” (1 Cor 11:25). The Greek word behind “covenant” in those words of institution is diathēkē — the same word that gives your Bible its name.

This is the chapter where those two uses are shown to be the same word doing the same theological work.

The Word

διαθήκη (diathēkē), pronounced dee-ah-THAY-kay. A feminine noun, first declension. From the verb diatithēmi (διατίθημι), “to arrange, to set in order, to dispose.” The basic sense of diathēkē is what someone has set in place — an arrangement, an ordered disposition, especially one with binding force.

In ordinary Greek usage of the New Testament era, diathēkē typically meant a last will and testament. When a Greek-speaking person of the first century heard diathēkē, the legal sense was the default: an instrument by which a person sets out how his property will be distributed after his death. The Greek word for an agreement between parties — what English-speakers usually mean by “covenant” — was synthēkē, not diathēkē. Synthēkē names a mutual contract negotiated between roughly equal parties; diathēkē names a one-sided arrangement laid down by one party for the benefit of others.

So when the Septuagint translators needed a Greek word for the Hebrew berit (בְּרִית) — the word for God’s covenants with His people — they chose diathēkē rather than synthēkē. The choice was theological. God’s covenant with Israel was not a contract between equals. It was God’s sovereign disposition, established on His own initiative, on terms He set, taking effect by His own action. Diathēkē captured that asymmetry in a way synthēkē could not. The Greek-speaking Jewish translators heard the divine covenants as more like a sovereign last will than a mutual agreement, and they passed that hearing on to the New Testament writers.

The New Testament inherits this. When the NT writers speak of diathēkē, they typically mean covenant in the berit sense — but they preserve the Greek connotations of unilateral disposition, of testamentary arrangement, of inheritance bequeathed rather than earned. And in some passages, especially in Hebrews, they exploit the dual sense deliberately.

Range of Meaning

In its New Testament usage, diathēkē covers:

• A covenant — a binding arrangement established by God with His people. The dominant sense, drawing on the Hebrew berit tradition.
• A last will and testament — the legal instrument by which a person disposes of property to take effect at death. Especially clear in Hebrews 9:15–17.
• A unilateral divine disposition — God’s sovereign arrangement of salvation, on His own initiative, for the benefit of those He calls.
• The Old and New Testaments as salvation-historical realities — the covenants God established with Israel under Moses, and the covenant established in Christ.

The two senses — covenant and testament — are not really separable in the New Testament’s use. They are the same word doing both jobs. When Christ speaks of the “new diathēkē in my blood,” He is announcing both a covenant established by God’s action and a testament that takes effect through His own death. The English translation often has to choose; the Greek does not.

Where You’ll Meet It

“For this is my blood of the covenant, which is poured out for many for the forgiveness of sins.” (Matthew 26:28, ESV)

The Words of Institution, in Matthew’s version. The diathēkē is being established in Christ’s blood. Worth noting: this is the new diathēkē (Luke and Paul add the word “new” explicitly), but it is also continuous with the old — Christ is fulfilling, not abolishing, the covenantal arc that runs from Abraham through Moses.

“And likewise the cup after they had eaten, saying, ‘This cup that is poured out for you is the new covenant in my blood.’” (Luke 22:20, ESV)

Luke’s version. The explicit word “new” appears. The new diathēkē is grounded “in” Christ’s blood — established by, given through, made effective by His death.

“In the same way also he took the cup, after supper, saying, ‘This cup is the new covenant in my blood. Do this, as often as you drink it, in remembrance of me.’” (1 Corinthians 11:25, ESV)

Paul’s preservation of the same saying. The Lord’s Supper is the meal of the new diathēkē. We will come to the “in remembrance of me” — anamnēsis — in Chapter 31. The point for the present chapter is just that the Supper is the place where Christians receive the new testament’s gifts.

“Therefore he is the mediator of a new covenant, so that those who are called may receive the promised eternal inheritance, since a death has occurred that redeems them from the transgressions committed under the first covenant. For where a will is involved, the death of the one who made it must be established. For a will takes effect only at death, since it is not in force as long as the one who made it is alive.” (Hebrews 9:15–17, ESV)

This is the passage where the dual sense of diathēkē becomes most theologically explicit. The author of Hebrews uses diathēkē twice, and in the second occurrence it clearly means “will” or “testament” in the legal sense — a will takes effect at the death of the one who made it. The “new covenant” Christ mediates is also a “last will” that has now taken effect through His death. Both senses are operating in the same passage. The English translation has to keep both in view; some translations explicitly switch from “covenant” to “will” within these three verses to capture the play, while others note the dual sense in a footnote.

“Brothers, I speak in a human way: even with a man-made covenant, no one annuls it or adds to it once it has been ratified… Now the promises were made to Abraham and to his offspring. It does not say, ‘And to offsprings,’ referring to many, but referring to one, ‘And to your offspring,’ who is Christ. This is what I mean: the law, which came 430 years afterward, does not annul a covenant previously ratified by God, so as to make the promise void.” (Galatians 3:15–17, ESV)

Paul argues from the diathēkē with Abraham — a covenant of promise, established with Abraham four centuries before the Mosaic law — to show that the law did not annul the promise. The Abrahamic diathēkē and the Mosaic diathēkē are not at war. The promise comes first; the law serves it; both are fulfilled in Christ.

“Who has made us sufficient to be ministers of a new covenant, not of the letter but of the Spirit. For the letter kills, but the Spirit gives life.” (2 Corinthians 3:6, ESV)

Paul on apostolic ministry. The new diathēkē has ministers who serve it. The contrast with the “letter” (the law as condemnation) versus the “Spirit” (the gospel that gives life) connects directly to the law/gospel distinction we treated in Chapter 11 on nomos.

“They are Israelites, and to them belong the adoption, the glory, the covenants, the giving of the law, the worship, and the promises.” (Romans 9:4, ESV)

Paul listing Israel’s privileges. The covenants — plural — belong to Israel. The Christian church does not replace Israel as the recipient of the covenants; we are grafted into the covenants God made with Israel through faith in Christ, the Jewish Messiah (Rom 11:17–24).