Old and New Testament: the difference and how they connect

The Old Testament is the collection Jesus and the first Christians already had; the New Testament is the collection written after him, by people who believed he had changed what the first one meant. In the Protestant canon that is 39 books and 929 chapters on one side and 27 books and 260 chapters on the other — 66 books and 1,189 chapters in all. The two are separated by language, by centuries, and by genre, and joined by a single argument that the New Testament makes on almost every page.

You can browse both, book by book, at the Bible index.

The word "testament" is misleading

It comes from the Latin testamentum, used to render a Hebrew and Greek word better translated covenant — a binding agreement, of the kind made between a king and a people. So the two halves are named after two covenants, not after two eras of divine mood, and certainly not after two Gods. That distinction is worth stating because the second-century teacher Marcion argued exactly that, and the churches rejected the idea; the reason the Christian Bible still opens with Genesis is that decision.

The New Testament's name for itself comes from a passage in the Old:

31 “Behold, the days come,” says Yahweh, “that I will make a new covenant with the house of Israel, and with the house of Judah, 33 “But this is the covenant that I will make with the house of Israel after those days,” says Yahweh: “I will put my law in their inward parts, and I will write it in their heart. I will be their God, and they shall be my people.

That is Jeremiah 31:31-33, written centuries before any of the New Testament existed.

The differences that actually matter

The length difference is the one people underestimate. The Old Testament is roughly three quarters of the Bible, and the habit of reading only the New produces a New Testament that is much harder to understand, since almost every important term in it — covenant, sacrifice, priest, kingdom, messiah, exile, temple — is defined in the other half.

The order of the books

Neither testament is arranged chronologically. Both are arranged by type.

The Old Testament, in the order most English Bibles print it:

1. Law — Genesis to Deuteronomy, five books, the story from creation to the edge of Canaan.
2. History — Joshua to Esther, twelve books, from settlement to exile and return.
3. Poetry and wisdom — Job, Psalms, Proverbs, Ecclesiastes, Song of Songs.
4. Prophets — Isaiah to Malachi, seventeen books, split by length into the "major" and "minor" prophets. The labels refer to size, not importance.

The New Testament:

1. Gospels — Matthew, Mark, Luke, John: four accounts of one life.
2. History — Acts, a single book, the movement's first decades.
3. Letters — twenty-one, from Romans to Jude, mostly written before the Gospels were finished.
4. Apocalypse — Revelation.

The Jewish Bible contains the same material as the Protestant Old Testament, grouped and ordered differently: Torah, Prophets and Writings, ending with Chronicles rather than Malachi. The change of ending changes the effect. A collection that closes with Chronicles ends with a decree to go up and rebuild; one that closes with Malachi ends with a prophecy of someone still to come.

Why some Bibles have more books

This is a real difference between Christian traditions, and it is not a matter of one side adding or another subtracting in bad faith.

• Protestant Bibles contain 39 Old Testament books, matching the Hebrew canon.
• Catholic Bibles contain 46, including Tobit, Judith, Wisdom, Sirach, Baruch, 1 and 2 Maccabees and longer forms of Esther and Daniel — books present in the ancient Greek translation of the Jewish scriptures used by early Christians. Catholics call them deuterocanonical; Protestants call them apocrypha.
• Orthodox Bibles include those and, depending on the church, further books still; the list is not identical across Orthodox communions.

All three traditions have the same 27-book New Testament. Where a passage in this site's articles depends on a book that is not in every canon, we say so.

The four threads that connect them

1. Promise and fulfillment

The New Testament quotes the Old constantly, and Luke has Jesus himself do it:

27 Beginning from Moses and from all the prophets, he explained to them in all the Scriptures the things concerning himself.

Luke 24:27. This is the thread with the most weight and also the one most easily overworked — not every Old Testament sentence is a coded prediction, and a study that treats it that way loses the original meaning of the text.

2. Covenant

Noah, Abraham, Moses, David: the Old Testament is structured around agreements. 2 Samuel 7 promises David a throne that lasts, and the Gospels open by calling Jesus the son of David. The New Testament's claim is not that the covenants failed but that they arrive somewhere.

3. One story, continued

Matthew opens with a genealogy for the same reason Luke sends his narrative back to Adam: the writers are not starting a story, they are continuing one. John 1 makes the same move by opening with the first words of Genesis.

4. The same God, described in continuity

1 God, having in the past spoken to the fathers through the prophets at many times and in various ways, 2 has at the end of these days spoken to us by his Son, whom he appointed heir of all things, through whom also he made the worlds.

Hebrews 1:1-2 states the relationship as one speaker over two periods, not two speakers.

What changes and what does not

Jesus states the relationship this way:

17 “Don’t think that I came to destroy the law or the prophets. I didn’t come to destroy, but to fulfill.

Matthew 5:17. Christians have disagreed for two thousand years about what "fulfill" implies for particular commands — food laws, sabbath, circumcision, the sacrificial system — and the disagreement runs through the New Testament itself, which records the argument rather than concealing it. What no major tradition holds is that the Old Testament was a mistake or that its God is a different God.

How to read them together

Three practical habits:

• Read a Gospel and a section of the Old Testament in parallel. The Gospels are dense with quotations, and reading Isaiah alongside Matthew makes half of them audible.
• When the New Testament quotes, go and look. Almost every quotation carries its original context with it, and the context is usually the point.
• Do not skip the Old Testament because it is long. Read the narrative spine first — Genesis, Exodus, Joshua, 1 and 2 Samuel, 1 and 2 Kings — and the prophets stop being cryptic, because you know what they are reacting to.

Genre matters as much here as chronology does; the literary genres of the Bible covers what each kind of book is doing. And the reading plan includes routes that alternate the two testaments instead of front-loading nine hundred chapters.