Concept

New Covenant

Intro

"What did Jesus mean when He lifted the cup at the Last Supper and called it the 'new covenant in My blood'?"

He was reaching back six hundred years to a promise from the prophet Jeremiah, and forward to His own death the next day.

In Jeremiah 31, God promises a new kind of arrangement with His people, different from the one He made with Israel at Mount Sinai through Moses. "Behold, days are coming, declares the LORD, when I will make a new covenant... not like the covenant which I made with their fathers... I will put My law within them and on their heart I will write it... they will all know Me, from the least of them to the greatest... I will forgive their wrongdoing, and their sin I will no longer remember" (Jeremiah 31:31-34).

Four features stand out in that promise.

It is internal, not external. The Old Covenant put the law on stone tablets. The New Covenant writes it on the heart. Obedience flows from a transformed inner life, not from an outer code being enforced.

It is universal among God's people. Under the Old Covenant, the priesthood mediated knowledge of God for the people. Under the New Covenant, every member of God's people knows Him directly.

Forgiveness is final. The Old Covenant sacrifices were repeated year after year on the Day of Atonement. The New Covenant brings a forgiveness God will not call back. "Their sin I will no longer remember."

It is sharply distinct from Sinai. Jeremiah says it explicitly: "not like the covenant which I made with their fathers."

When Jesus took the cup at the Last Supper and said, "This cup which is poured out for you is the new covenant in My blood" (Luke 22:20), He was claiming that the moment Jeremiah had foreseen had arrived. His death the next day would ratify the new arrangement. The blood of the new covenant would not be the blood of bulls and goats. It would be His own.

The book of Hebrews works this out in detail. Jesus is the mediator of a better covenant (Hebrews 8). His sacrifice does what the Old Covenant sacrifices could not do (Hebrews 9-10). He intercedes for His people as the eternal High Priest, in the order of Melchizedek, not Aaron (Hebrews 7).

For Christians, the practical results show up at every layer of the faith. The Spirit indwells believers, writing the law on the heart (Romans 8:9-11). Every believer has direct access to God through Christ, not through a human priest (Hebrews 4:16). Forgiveness is once for all, secured by the cross (Hebrews 10:10). The Lord's Supper, repeated in Christian worship, remembers the new covenant inauguration in Christ's blood.

For the contrast with the Old Covenant, see that page. For the source dialogue that triggered this page, see Are Christians Still Under The Law (ris3n).

In full

The covenantal framework promised in Jeremiah 31.29-34 and inaugurated by Jesus' blood at the Last Supper (Luke 22.19-20: "this cup which is poured out for you is the new covenant in My blood"). Where the Sinai covenant was a blood-sealed bond mediated through Moses and maintained by Levitical sacrifice, the New Covenant is sealed in Christ's own blood, internalizes the law in the believer's heart, secures complete forgiveness ("I will remember their sin no more"), and rests on the eternal high-priestly mediation of Christ in the order of Melchizedek.

Core features (per Jer 31:31-34)

Internal, not external, "I will put My law within them and on their heart I will write it." Obedience flows from inward transformation rather than from external code.
Universal among the people of God, "they will all know Me, from the least of them to the greatest." No mediating priest-class required for the basic knowledge of God.
Definitive forgiveness, "I will forgive their wrongdoing, and their sin I will no longer remember." Not the repeated-and-symbolic forgiveness of the Day of Atonement cycle, but a final settlement.
Distinct from Sinai, explicitly framed as "not like the covenant which I made with their fathers."

Inauguration

Last Supper, Jesus identifies the cup as "the new covenant in My blood" (Luke 22:20; cf. 1 Cor 11:25), echoing Moses' covenant-blood at Sinai (Exod 24:6-8) and rerouting it through Himself.
Crucifixion, the actual blood-shedding that ratifies the covenant.
Resurrection and exaltation, installs Christ as the New Covenant high priest forever (Heb 7:24-25).

Relation to the Old Covenant

Heb 8:13, the new makes the first "obsolete." The dominant New Testament framing is supersession: the Old Covenant is not run in parallel with the New, it is replaced as the governing covenantal system.
Heb 7:11-12, the change of priesthood (Levitical → Melchizedekian) entails a change of law. The two covenants cannot coexist as parallel governing structures.
Gal 3:24-25, pedagogical relation: the Law was a tutor leading to Christ; once Christ comes the tutor's role is completed.

Tensions across Christian traditions

How sharply the Old Covenant is "replaced" varies considerably:

Reformed covenantal, distinguishes one covenant of grace administered differently across redemptive history; the New Covenant is its consummate administration. Moral law (Decalogue) carries forward; ceremonial / civil are abrogated. The "obsolete" of Heb 8:13 applies to the administrative form, not to the unity of God's saving covenant.
Dispensational / supersessionist (the position of Are Christians Still Under The Law (ris3n)), sharp break: the Old Covenant is replaced wholesale as a governing system.
New Covenant Theology (a third option), affirms a clean break with the Mosaic Law as a covenant code while holding that Christ's law (re-stated, not derived from Sinai) governs Christian ethics.
Hebrew Roots / Messianic / Theonomy, minimize or deny supersession; the Torah remains binding to varying degrees.

The codex records each fairly without arbitrating. Add positions and inline tensions as further sources are ingested.