The New Testament vs. New Covenant?

What is the difference between “Testament” and “Covenant”? In the Western world, many people are familiar with a “Final Will and Testament” — a legal document read when someone dies. The document expresses the wishes of the deceased, often in connection with estate and inheritance. As a unilateral declaration of one’s will, a “testament,” in this sense, is not the same as a "covenant," “contract” or “pact,” which necessitates an agreement between two or more parties. It's not hard to see the misalignment between the ideas of "covenant" and "testament."

The author of the Book of Hebrews makes an appeal to this Greek term to show that a “testament” (διαθήκη; diatheke) is initiated only after death (Heb 9:16-17). The English theological term “New Testament” comes from the Latin Novum Testamentum – The Latin for “New Testament” which is a translation of the Greek phrase καινὴ διαθήκη (kaine diatheke) that appears in the Septuagint (Jer 31:31 LXX; cf. Lk 22:20). Yet, upon closer examination, the original Hebrew term for “covenant” (בְּרִית; berit) does not line up to the idea of “testament” (διαθήκη; diatheke) exactly. So why would this particular Greek word be used in Luke, Hebrews, and 1 Corinthians (Lk 22:20, Heb 8:8; 9:11–15, Cor 11:25)? Hard to say, but perhaps the authors merely followed in the footsteps of the translators of the Jewish Bible into Greek who felt that this was the best word to translate the Hebrew “covenant” (בְּרִית; berit). We can't know this for sure.