Since I am not a Christian I am not entirely clear on this subject, but hopefully someone will inform me.
My understanding, recently, is that through Jesus, mankind has a covenant with god in the NT which supersedes the one described in the OT.
My first question is: Is this a universally held belief, or is it specific to certain forms of Christianity?
Second question: Does the 2nd covenant have to explicitly mention a subject already dealt-with in the OT for it to be considered part of the 2nd covenant? Or, are aspects of the OT covenant considered to still be valid until or unless otherwise dictated in the NT?
The Christian idea, broadly, is that all of God's covenants and promises had as their purpose and goal, their end, in Christ. That includes the Covenant God made with the Israelites in Sinai.
Thus all of God's promises and covenants before Christ are subsumed into Christ, subsisting in Him and the new covenant. God's promise to Abraham, "I will make you a father of many nations" for example is subsumed into Christ, the point of it is Christ, whom St. Paul calls the "Seed of Abraham". Christ is the Promise. Likewise the covenant established through Moses to the nation of Israel to set them apart as a special people is fulfilled, find its chief end in Christ.
We say that God called Abraham out from Ur and gave him the promise of a child, to be a father of many, for Christ.
We say that God chose Moses, and established a nation, and gave them the Torah for the sake of Christ.
For the Christ came, the fulfillment and the reason for which all these things previously took place.
The chief end of establishing a nation and giving them a code of laws by which to live and function as that nation wasn't for its own end; but rather for the coming of the Messiah from that nation who "universalizes" the nation to incorporate all people, to bring all the nations together. To fulfill--make perfect--the Law that was given.
The peculiarities of that Covenantal Law--the Torah--were for a very specific group of people, a distinct nation. God didn't give it to the Hittites, the Aztec, or the Chinese; but to a very specific nation of people.
That Covenant, that nation, those promises are all brought to their fullness in Jesus, the Messiah. And in that same Jesus goes out the Gospel to all nations, that He was crucified and that He has risen from the dead as Lord, as the victorious one over death, to take all men and bring them under God the Father, to make all men children of God, to make of all nations one people, established in the Messiah, the One who has destroyed sin and death in His own body, and has been raised, and who is seated above all thrones, powers, and dominions, above all kings and lords, and who gathers all under Him, so that He might present all before God, justifying them, saving them, and delivering them through the judgment and destruction of this present age and on the other side, raised up even as He has been raised, to live and dwell with God forever in the World to Come.
As an example: Christians believe that God so ordered the offerings of bulls, goats, and lambs not as though these are something in and of themselves (consistently God says He takes no pleasure in the smell of burnt offerings, but rather in a contrite and repentant heart); and that these sacrifices are intended as shadows of the Reality, Jesus the Messiah, whose death is real atonement. Reconciling God and man together by His destroying the powers of sin, death, hell, and the devil. Not as though the death of a man is pleasurable to God, or that God is bloodthirsty and needs blood to be spilt; but rather that in dying Jesus undoes death. Death and resurrection go hand-in-hand; that He is raised so as to proclaim that Death is dead, for He has slayed it in His own body, for the sake of all men and all creation which labors under the bondage, the captivity, the slavery of death.
Which is precisely why we do not believe the Torah is for everyone, or that we are to observe it. Its statutes were for a specific people, a specific nation, for a time that preceded and yet ultimately points toward the coming of the Christ. And we confess that He has come.
-CryptoLutheran