The New Covenant (Ancient Greek: διαθήκη καινή, romanized: diathḗkē kainḗ) is a biblical interpretation which was originally derived from a phrase in the Book of Jeremiah (Jeremiah 31:31–34), in the Hebrew Bible (or the Old Testament of the Christian Bible). Generally, Christians believe that the promised New Covenant—new relationship with God—was instituted at the Last Supper as part of the Eucharist, which, in the Gospel of John, includes the New Commandment.
Most Christians believe that Jesus is the mediator of the New Covenant, and they also believe that the blood of Christ, which was shed during his crucifixion, is the only blood sacrifice which is required by the covenant. Based on the biblical passage in the Epistle to the Hebrews (9:16–17) which reads that, "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." Protestants tend to believe that the New Covenant came into force with the death of Jesus the Christ, and the commentary to the Roman Catholic New American Bible also says that Christ is the "testator whose death puts his will into effect".