The Old Testament and New Testament Explained
Posted by Brother Oscar
One story in two acts — and the word that holds them together
Most Christians have held a Bible in their hands for years without pausing to ask what the word "testament" actually means. It does not mean "book." It does not mean "era." It is a translation of a Hebrew and then Greek word for covenant — a binding agreement between God and his people. The Old Testament gathers the scriptures of ancient Israel, shaped by a series of covenants: with Noah after the flood, with Abraham and his descendants, with Israel at Sinai, and with David and his royal line. The New Testament is the new covenant that Jeremiah promised God would make, not on stone but on human hearts, and that Christians understand was established through Jesus Christ.
Understanding that single word changes how you read everything that follows. The two Testaments are not simply "before Jesus" and "after Jesus." They are two movements of one covenant relationship — promise and fulfilment, shadow and substance, the same God working through every chapter. The writers of the New Testament quote the Old hundreds of times, not as background reading but because they believed the story was continuous. Jesus himself put it plainly in the Sermon on the Mount, delivered on a hillside in Galilee that still overlooks the same sea: "Do not think that I have come to abolish the Law or the Prophets; I have not come to abolish them but to fulfil them" (Matthew 5:17).
What follows explains what the Old Testament and New Testament each contain, how their books are arranged, why the number of books differs between Catholic and Protestant Bibles, and how the biblical canon we read today was formed. The relationship between the Old Testament and New Testament is not just a structural question — it is the central claim of the Christian faith.
What the Word "Testament" Actually Means
The English word "testament" comes from the Latin testamentum, the word used to translate the Greek diatheke, which itself translated the Hebrew berit: covenant. The terms Vetus Testamentum (Old Testament) and Novum Testamentum (New Testament) were already in use in Latin Christianity before Jerome; the theologian Tertullian, writing in Carthage around the turn of the third century, was among the first to apply them consistently to the two collections of Scripture. By the time Jerome produced the Vulgate in the late fourth century, the terminology was already established — though Jerome's translation gave those names their definitive Latin form for the Western Church.
A covenant in the ancient Near East was not a casual agreement. It was a solemn, binding bond — often sealed in blood, marked by a sign, and carrying obligations on both parties. The Bible describes several of these: God's covenant with Noah, marked by a rainbow; the covenant with Abraham, sealed by circumcision and the promise of descendants and land; the covenant at Sinai with Israel, expressed in the Torah; and the covenant with David, promising an enduring dynasty. When Christians speak of the Old Covenant and the New Covenant, they are using language the biblical writers themselves used. The prophet Jeremiah, writing in the seventh century BC, recorded a divine promise that has shaped Christian reading of Scripture ever since:
"The days are coming, declares the Lord, when I will make a new covenant with the people of Israel and with the people of Judah."
— Jeremiah 31:31
The New Testament writers understood this passage as the promise Jesus fulfilled. The word diatheke appears in the accounts of the Last Supper, when Jesus takes the cup and says this is the "new covenant" in his blood (Luke 22:20, 1 Corinthians 11:25). The Letter to the Hebrews quotes Jeremiah directly and at length, arguing that the new covenant has made the first one obsolete. This is the theological logic behind the two-part structure of the Christian Bible: old covenant and new covenant, the same God, one continuous story.
The Old Testament: Structure and Contents
The Old Testament is the Christian name for the collection of sacred texts that the Jewish people had already gathered over more than a thousand years. Jews call the same body of writing the Tanakh — an acronym formed from its three sections: Torah (Teaching), Nevi'im (Prophets), and Ketuvim (Writings). The content is largely the same; what differs is the arrangement and, for Catholic and Orthodox Christians, the addition of further books (discussed below).
The arrangement Christians are most familiar with derives not from a deliberate theological decision but from the influence of the ancient Greek translation of the Hebrew scriptures known as the Septuagint. Where the Hebrew Bible groups books into three sections, the Septuagint organised them by genre into four: Law, History, Poetry and Wisdom, and Prophets. Jerome followed a similar arrangement in the Vulgate, and most Christian Bibles today reflect that four-part pattern. One visible consequence is that the Christian Old Testament ends with the books of the prophets — Malachi in most Protestant and Catholic editions — giving it a forward-looking quality. The Hebrew Bible, by contrast, ends with Chronicles and Cyrus's decree allowing the exiles to return, closing on a note of historical restoration rather than prophetic anticipation.
Those four sections, as most English Bibles present them, are: the Law (the five books of Moses, also called the Pentateuch or Torah — Genesis through Deuteronomy); the Historical Books (Joshua through Esther or Nehemiah, depending on the tradition); the Poetry and Wisdom Books (Job, Psalms, Proverbs, Ecclesiastes, Song of Solomon and, in Catholic editions, Sirach and Wisdom); and the Prophets, both major and minor (Isaiah through Malachi). The specific books within each section and their order vary somewhat between Catholic, Orthodox, and Protestant editions.
The great events of the Old Testament did not happen at a distance from the land. The Exodus led through the Sinai peninsula; the covenants were made at mountains and altars still visited today. The psalms were composed in and around Jerusalem, in the city where David built his capital. The prophets preached in the streets of cities whose ruins survive. The complete story of the Holy Land's biblical geography traces the places where these texts took root in the soil of actual history.
The New Testament: Structure and Contents
For the great majority of Christians — Catholic, Orthodox, and Protestant — the New Testament consists of 27 books, and there is no disagreement among them on this point. The differences between Christian Bibles are concentrated in the Old Testament. One significant exception is the Ethiopian Orthodox Tewahedo Church, whose broader canon includes additional books of church order alongside the familiar 27, making its New Testament total 35. The Tewahedo canon is the largest in Christendom, and its history reflects the diversity of early Christian textual traditions in East Africa.
Those 27 familiar books fall into four broad groups. The Gospels — Matthew, Mark, Luke and John — are four accounts of the life, teaching, death and resurrection of Jesus. They are not biographies in the modern sense; they were written as proclamation, shaped by the faith of communities that proclaimed Jesus's resurrection before any of the Gospels reached their written form. Each Gospel has its own voice, its own intended audience, and its own angle on the same events. The Gospels are followed by the Acts of the Apostles, which continues Luke's account into the early church, recording the work of Peter and Paul across the Mediterranean world.
The Letters — or Epistles — make up the largest section by book count: twenty-one letters written to early Christian communities and individuals. Most are attributed to Paul, and several are among the earliest documents in the New Testament, written before any of the Gospels reached their final form. Paul's letter to the Romans is a sustained theological document. His letters to the Corinthians are pastoral responses to specific crises in a specific congregation. The final New Testament book, the Book of Revelation — also called the Apocalypse — is a text of prophetic vision addressed to seven churches in Asia Minor, written in the genre of Jewish apocalyptic literature, rich with imagery drawn from the Old Testament.
The New Testament was written in Koine Greek — the widely shared language of the eastern Mediterranean in the first century. Several of its authors came from Jewish communities where Aramaic, Hebrew and Greek were used in different settings, while Greek provided a language through which these writings could circulate across much of the Roman world, from Jerusalem and Antioch to Corinth and Rome. The Septuagint, the ancient Greek translation of the Hebrew Scriptures, was already widely used, and New Testament authors frequently quote or echo its language.
The Biblical Canon at a Glance
The following table summarises what the major Christian traditions include in their Bibles and where the differences lie. The Old Testament column is where the differences are concentrated; the familiar 27-book New Testament is shared across the traditions shown in the first three rows, with the Ethiopian tradition noted separately.
| Tradition | Old Testament | New Testament | Total Books | Key difference |
|---|---|---|---|---|
| Protestant | 39 books | 27 books | 66 | Follows the Hebrew Bible; excludes deuterocanonical books |
| Catholic | 46 books | 27 books | 73 | Includes 7 deuterocanonical books from the Septuagint tradition |
| Eastern Orthodox | 49+ books | 27 books | 76+ | Typically includes additional texts; varies by autocephalous church |
| Ethiopian Orthodox Tewahedo | 46+ books | 35 books | 81 | Broader NT includes books of church order alongside the 27 familiar books |
The entire debate about which Bible has "more books" concerns the Old Testament for most traditions — and specifically a collection of texts whose dates and original languages vary considerably, written during the period between the Hebrew prophets and the New Testament era.
Why Catholic and Protestant Bibles Have Different Numbers of Books
In the first century, Jewish communities in Egypt and across the Greek-speaking world used a Greek translation of their Scriptures known as the Septuagint, named for the tradition that seventy (or seventy-two) scholars had produced it in Alexandria. The Septuagint included a number of books not found in the Hebrew Bible — texts that came to circulate in Greek, even when some had originally been composed in Hebrew or Aramaic. These included Tobit, Judith, the books of Maccabees, Wisdom, Sirach and Baruch. The early Church used the Septuagint widely, and so these texts circulated in Christian communities from the beginning.
Their original languages were varied. Sirach was written in Hebrew — Hebrew manuscripts have been recovered and the Greek translator's prologue says explicitly that his grandfather composed it in Hebrew. 1 Maccabees was also originally in Hebrew, surviving only in Greek translation. Tobit and Judith were written in Hebrew or Aramaic — Aramaic fragments of Tobit were found among the Dead Sea Scrolls. 2 Maccabees and Wisdom were composed in Greek. Baruch is more complicated, with some sections possibly translated from Hebrew or Aramaic. The claim that all these books were "originally written in Greek" is not accurate.
The question of whether they were Scripture was genuinely contested for centuries. Some early Church writers regarded them as fully authoritative; others — including Jerome — expressed reservations, preferring to distinguish them from the books found in the Hebrew Bible. Jerome's position was complicated. He personally translated Tobit and Judith from Aramaic, but left Wisdom, Sirach, Baruch, and the books of Maccabees in their existing Old Latin form rather than producing new translations; those books passed into the Vulgate through earlier Latin versions. For a thousand years they circulated alongside Jerome's reservations, expressed in his prefaces, while the Latin Church read and preached from them as Scripture.
The division that most people encounter today came during the Protestant Reformation of the sixteenth century. Martin Luther and the Reformers, in returning to the Hebrew biblical text as their Old Testament standard, set these books aside — placing them in a separate section labelled "Apocrypha" rather than removing them entirely from their editions at first. They remained in most Protestant Bibles for another century or more before being omitted from printed editions altogether.
The Catholic Church, responding at the Council of Trent (1546), formally defined these books as fully canonical Scripture, using the term deuterocanonical — a second reception, not a second rank. Eastern Orthodox churches, drawing on the Septuagint tradition, accept at least these seven and in some traditions more. The result is that a Catholic reading the catechism will find it quoting from Wisdom and Sirach; a Protestant reader may never have encountered those books at all.
How the Canon Was Formed
The word canon comes from the Greek kanon, meaning rule or measuring stick — the standard by which writings were judged authoritative. The formation of the biblical canon was not a single decision made on a single day. It was a process that ran across centuries, beginning with the recognition of the Torah in Jewish communities, continuing through the gathering of the prophetic writings, and concluding — for the New Testament — only in the late fourth century.
For the Old Testament, the Torah and the core prophetic books were treated as Scripture across Jewish communities by the first century AD. The boundaries of the Writings were less universally settled; some books — Ecclesiastes, the Song of Songs, Esther — were still being discussed in certain quarters. The picture of a cleanly "closed" Hebrew canon by the time of Jesus is an oversimplification; what was settled was the central, most authoritative core, while the edges of the collection retained some fluidity.
The New Testament took longer. The letters of Paul began circulating in the 50s AD, within twenty years of the crucifixion. The Gospels reached their written form between approximately 70 and 100 AD. By the end of the first century, most of what became the New Testament was in wide use, and there was already broad agreement about the core: the four Gospels, the letters of Paul, the Acts of the Apostles. Agreement on the edges — Hebrews, James, 2 Peter, 2 and 3 John, Jude, and especially Revelation — took longer, and some were disputed in particular regional churches for another century or more.
The first surviving document to list all 27 New Testament books — and only those 27 — was written by Athanasius of Alexandria in his Easter letter of AD 367. His list was not a new decision but a formal endorsement of what most churches had already come to accept. The regional Synod of Hippo (393) and the regional Council of Carthage (397), both held in North Africa, ratified the same list. These were not ecumenical councils with authority across all Christianity, but their endorsement carried weight in the Latin West and reflected a consensus that had been forming for generations. By then, the councils were affirming a de facto agreement rather than creating one.
A significant earlier document is worth knowing. The Muratorian Fragment, a Latin text discovered in Milan in 1740 and dated by most scholars to the late second century (around 170–200 AD), lists most of the New Testament books that form the familiar canon today — evidence that wide agreement on the core existed more than a century before the councils formally ratified it. The fragment is damaged and incomplete, but it shows the four Gospels, Paul's letters, Acts, Revelation and several of the catholic epistles already treated as authoritative in Rome at that early date.
How the Old and New Testaments Fit Together
The early Church wrestled with a real question: what was the relationship between the Scriptures they had inherited from Judaism and the new writings about Jesus? A teacher named Marcion, active in Rome around 140 AD, gave a radical answer — he rejected the Old Testament entirely, arguing that the God of Israel was a lesser deity, entirely separate from the Father of Jesus. The Church rejected Marcion decisively. His challenge clarified something the Church had always implicitly believed but now stated clearly: the two Testaments belong together, and the God of both is the same God.
That conviction gave Christian biblical reading its characteristic shape. The Old Testament is not merely background to the New; it is Scripture in its own right, authoritative and life-giving, while also being read in the light of what came after. Christians read the Psalms as prayers, as prophecy, and as the prayer-book of Jesus himself — who died with Psalm 22 on his lips and prayed through words that had been sung in the Temple for centuries. They read Isaiah's suffering servant as pointing forward to Christ, and Genesis as opening a story that the New Testament brings to its first great turning point.
The technical term for this approach — reading the Old Testament as pointing toward and being fulfilled in the New — is typological reading. The Passover lamb is a type of Christ; the manna in the wilderness is a type of the Eucharist; the crossing of the Red Sea is a type of Baptism. The New Testament writers themselves use this language. Paul tells the Corinthians that the events of the Exodus "were written down as warnings for us, on whom the culmination of the ages has come" (1 Corinthians 10:11). The Letter to the Hebrews spends eleven chapters demonstrating how the entire priestly system of the Old Testament was a shadow of what Christ accomplished.
None of this means the Old Testament is read as merely allegorical or as having no meaning in its own right. Jewish readers find rich and sufficient meaning in the Hebrew Scriptures without the lens of the New Testament — and Christians reading attentively have always recognised this. The relationship between the Testaments is one of the most fertile and ongoing questions in biblical theology, with serious scholars in every century adding to the conversation.
For anyone who wants to begin engaging with Scripture as a living practice rather than a historical document, the ancient method of Lectio Divina — slow, prayerful reading of a chosen passage — offers a way into both Testaments that requires no expertise, only attention and a willingness to stay with the text long enough for it to speak.
Sources and Further Reading
This article draws on the following primary, institutional, and scholarly sources. Readers who want to go deeper on any of the topics covered will find these reliable starting points.
- USCCB — Questions about the Bible — The United States Conference of Catholic Bishops' plain-language guide to the Catholic biblical canon, including the distinction between Catholic and Protestant Old Testaments.
- USCCB — Do Translations Matter? — Explains the deuterocanonical books, their presence in the Catholic canon, and what to look for in a Catholic edition of the Bible.
- Encyclopaedia Britannica — Biblical Canon — A scholarly overview of how the canon of Scripture developed across Jewish and Christian communities.
- BYU Religious Studies Center — The Canonization of the New Testament — A detailed account of the process by which the 27-book New Testament canon was recognised, including the roles of Athanasius, the Muratorian Fragment, and the councils.
- Christian History Magazine — How We Got Our Old Testament — Accessible survey of how the Old Testament was gathered, arranged, and transmitted, including the Septuagint's four-part structure.
- Ethiopian Orthodox Tewahedo Church — The Holy Scriptures — The church's own listing of its 81-book biblical canon, including the 35 New Testament books.
Frequently Asked Questions
What is the difference between the Old Testament and the New Testament?
The Old Testament contains the sacred writings of ancient Israel — the law, history, poetry, and prophecy that formed the faith of the Jewish people before Christ. The New Testament records the life, teaching, death and resurrection of Jesus, and the writings of the apostles. Christians read the two together, understanding the New as the fulfilment of what the Old promised.
How many books are in the Old Testament and the New Testament?
For most Christians, the New Testament contains 27 books and the Old Testament varies by tradition: Protestant Bibles contain 39 books, Catholic Bibles 46, and Eastern Orthodox Bibles typically 49 or more depending on the church. The Ethiopian Orthodox Tewahedo Church has a broader canon of 81 books in total.
Why do Catholic Bibles have more books than Protestant Bibles?
Catholic Bibles include seven books — Tobit, Judith, 1 and 2 Maccabees, Wisdom, Sirach and Baruch — found in the ancient Greek Old Testament tradition but not in the Hebrew Bible. The Protestant Reformers in the sixteenth century set these aside, following the boundaries of the Hebrew canon. Catholics call them deuterocanonical; Protestants call them the Apocrypha.
What does the word 'testament' mean in the Bible?
Testament comes from the Latin testamentum, used to translate the Greek diatheke, which means covenant. Early Latin Christian writers including Tertullian used the terms Vetus Testamentum and Novum Testamentum before Jerome, who gave them their definitive form in the Vulgate. The covenants of Scripture — with Noah, Abraham, Israel, David, and finally the New Covenant in Christ — are what give the Bible its two-part shape.
When was the New Testament canon finalised?
Athanasius of Alexandria listed all 27 familiar New Testament books in his Easter letter of AD 367 — the earliest surviving document with that exact list. The regional Synod of Hippo (393) and the regional Council of Carthage (397) in North Africa endorsed the same books, ratifying what had by then become the broad consensus of the churches.
Is the Old Testament relevant to Christians?
Christians have consistently read the Old Testament as essential Scripture rather than a preface to be set aside. The New Testament quotes it hundreds of times, and Jesus himself said he came not to abolish the Law or the Prophets but to fulfil them (Matthew 5:17).
Closing Reflection
Jerome settled in Bethlehem in 386 AD and spent the remaining decades of his life there, studying, translating, and writing in the shadow of the place where Christ was born. The cave associated with his work lies adjacent to the Grotto of the Nativity, and pilgrims have venerated both sites for centuries. Whatever drove him to choose that place, the result was a Latin Bible that shaped Western Christianity for more than a thousand years.
What he produced — and what the councils, scribes, and communities across five centuries had recognised and gathered — was not two books, but one long conversation between God and humanity. The Old Testament and the New Testament hold together not because anyone decided they should, but because the promise and its fulfilment belong to the same story. Readers who slow down long enough to follow that thread from Genesis to Revelation usually find that the conversation is still going.
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