The difference between the Old and the New Testament

In English, a testament is the document in which someone disposes of their property after death. That is not the sense here. The word reached us through a chain of translations: the Hebrew term denotes a pact, a covenant, a formal agreement between two parties; the Greek rendered it with a term that serves both for covenant and for testamentary disposition; Latin chose the word that became “testament” in English. The original sense running through all of it is covenant.

Reading “Old Covenant” and “New Covenant” in place of the two titles changes the understanding immediately — because the Bible is not divided between a book of law and a book of grace, but between two moments of a relationship under covenant.

One detail many people do not know, and which prevents misunderstanding: the expression “new covenant” is not a Christian coinage. It appears inside the Old Testament, in a prophet, centuries earlier. When Christians began using it, they were picking up vocabulary that already existed in the text they had inherited.

The Old Testament is about three times the size of the New. There are 39 books common to all Christian editions — which the Hebrew Bible counts as 24, because it groups some of them differently — plus the seven deuterocanonical books present in Catholic and Orthodox editions. The New Testament has 27 books, and those 27 are exactly the same in every Christian tradition, with no divergence at all.

The distance in time is just as disproportionate. The Old Testament material accumulated across many centuries; the entire New Testament was written within a period most scholars place in a few decades of the first century, even though the dating of each book is debated. One part is the library of a people across its history; the other is the concentrated output of one generation reacting to an event.

The genres differ in the same proportion. The Old Testament has historical narrative, legal code, poetry, proverb and prophetic oracle. The New has four ancient biographies, an account of expansion, a large block of letters and a visionary book. There is nothing in the New Testament equivalent to the Psalms, and nothing in the Old equivalent to a pastoral letter — and reading the two with the same expectation of language is the most common cause of bewilderment.

One observation settles a great deal: when the authors of the New Testament write “the Scriptures”, they mean the Old Testament. The New did not yet exist as a collection, and the Bible of the first Christians was exactly the Bible of Israel.

The dependence is quantitative and structural. The New Testament quotes the Old hundreds of times and alludes to it far more often than it quotes. Central vocabulary — covenant, sacrifice, lamb, temple, messiah, kingdom, exodus — is not defined in the New Testament; it is used on the assumption that the reader already knows what it means, because the meaning was built in the earlier books.

The practical consequence is direct: whoever reads only the New Testament grasps the story but reads a good share of the sentences at half strength. And whoever concludes from that the Old Testament is mere supporting material inverts the relation — it is the text the New Testament authors treated as Scripture, not an appendix to it.

Here the descriptive part ends and the disputed part begins. The question is not whether the Old Testament still holds as Scripture — on that every Christian tradition agrees. The question is how the two parts articulate: what of the Old remains in force, in what sense the New “fulfils” it, and what exactly changed.

Two New Testament passages mark the poles of the debate, and both are in the same canon. One states that the coming of Jesus did not come to loosen the Law and the Prophets but to bring them to their fullness. The other, in a different letter, says that in speaking of a new covenant the former has been made old. Any serious reading has to account for both, and the traditions do so in different ways — which is precisely the divergence.

The note below sets out the main readings. They do not distribute cleanly between Catholics and Protestants: the first two cut across both groups, and the third is more common in some Protestant currents than in others. Labelling the divergence as “Catholics think X, Protestants think Y” would be simpler and would be false.

There is a point at which the discussion stops, and it is a historical one. In the second century, Marcion proposed the most radical solution available: discard the entire Old Testament, along with much of the New, on the argument that the God portrayed there was not the God of the Gospel. The proposal was coherent and settled the problem of difficult passages in one stroke.

It was rejected. And it was rejected so widely that it became one of the rare points of agreement between traditions that disagree about almost everything else: no historic Christian church accepts splitting the two Testaments into two Gods, or treating the Old as disposable revelation.

This works as a practical reading criterion. When an explanation of a difficult Old Testament passage arrives, even without saying so, at the conclusion that the deity described there and the one revealed in the Gospel are two different beings, it is re-enacting an exit the Church refused in the second century — and refused precisely because it saw the price was too high.

There is a way of telling the relation between the Testaments that sounds natural and is problematic: that the people of the first covenant were swapped for the people of the second. The problem is not one of contemporary sensibility — it is textual. The New Testament deals with the subject directly, and what it states is the opposite.

The central passage is in Romans, in a stretch where Paul is discussing exactly this question. His argument ends in a categorical statement about the irrevocability of God’s call, and it is that formulation twentieth-century Christian documents drew on when treating the theme — among them the Catholic conciliar declaration of 1965, which cites it expressly.

For reading, the consequence is simple: the arrival of the New Testament is presented by the New Testament itself as enlargement, not as substitution. Keeping that in view avoids most of the formulations that age badly.

The difference in genre calls for a difference in method, and that is the part you can use day to day. Old Testament historical narrative is read in long blocks, following the arc — an isolated chapter there almost never works. Legal code is read by asking who it was addressed to and what it regulated in that society, before asking what it means today. A prophet is read against the backdrop of the political crisis he answers, which is why prophets come after the historical books in most reading plans.

In the New Testament, a Gospel is read whole, start to finish, because each one has its own structure and its own point of arrival. A letter is read as a letter: one side of a conversation, answering questions that are not written down. And Revelation asks the same care as any ancient visionary literature, whose code of images was known to its first readers and is not known to today’s.

One last observation about direction of reading. The New clarifies the Old, and the Old gives density to the New — both directions work. What does not work is only going one way: whoever only goes from the New to the Old ends up seeing there only what confirms what they already knew, and whoever only goes from the Old to the New misses the key the New Testament authors were themselves using.