What is the difference between the Old and New Testament?

One Book, Two Acts

The Bible is not a collection of disconnected religious writings. It is a single, unified narrative — one story told across two major sections. The Old Testament (OT) sets the stage: creation, fall, covenant, law, prophecy, and the long expectation of a coming deliverer. The New Testament (NT) reveals the fulfilment: God himself enters the story in human form, accomplishes what the whole first act was pointing toward, and sends his people out to announce it to the world.

Understanding the relationship between the two Testaments is one of the most important keys to reading the Bible well. Misread it, and you end up with either a God who changed his mind between the books, or a New Testament that floats free of its roots. Neither is accurate.

What the Old Testament Is

The Old Testament is the larger section — 39 books in the Protestant canon, 46 in the Catholic canon (which includes the deuterocanonical books). It spans roughly 1,500 years of history and is written primarily in Hebrew, with small portions in Aramaic.

It covers several broad categories:

• The Law (Torah / Pentateuch): Genesis, Exodus, Leviticus, Numbers, Deuteronomy — the first five books, attributed to Moses. They cover creation, the fall of humanity, the flood, the calling of Abraham, the Exodus from Egypt, and the giving of the Mosaic Law at Sinai.
• History: Joshua through Esther — the story of Israel entering the Promised Land, the period of the judges, the rise and fall of the monarchy (Saul, David, Solomon), the division of the kingdom, exile to Babylon, and eventual return.
• Poetry and Wisdom: Job, Psalms, Proverbs, Ecclesiastes, Song of Solomon — reflections on suffering, worship, wisdom, and human experience in light of God's character.
• Prophecy: Isaiah through Malachi — the major and minor prophets calling Israel back to covenant faithfulness and looking forward to a coming king and deliverer. Many of these prophecies are quoted in the New Testament as fulfilled in Jesus.

The central thread running through all of it is covenant — God's binding commitment to his people, progressively revealed through Noah, Abraham, Moses, and David. Each covenant builds on the last and moves the story forward. The OT ends with the prophet Malachi and then a 400-year silence before the New Testament opens.

What the New Testament Is

The New Testament contains 27 books, all written in Greek, most within 60 years of the crucifixion of Jesus. It falls into four categories:

• The Gospels: Matthew, Mark, Luke, and John — four accounts of the life, death, and resurrection of Jesus, each written for a different audience and with a different emphasis.
• Acts: Luke's account of the early church from Pentecost through Paul's arrival in Rome — the story of how the gospel spread from Jerusalem to the ends of the earth.
• The Epistles (Letters): Romans through Jude — letters written by Paul, Peter, James, John, and Jude to specific churches or individuals, addressing theology, ethics, pastoral concerns, and doctrinal disputes.
• Revelation: An apocalyptic vision given to the Apostle John on the island of Patmos, addressing the suffering of the church and the ultimate victory of Christ over all evil.

The New Testament's central claim is that Jesus of Nazareth is the fulfilment of everything the Old Testament promised — the prophet like Moses (Deuteronomy 18:15), the son of David who rules forever (2 Samuel 7:12–13), the suffering servant of Isaiah 53, the new covenant mediator of Jeremiah 31.

How They Relate: Promise and Fulfilment

The most important relationship between the two Testaments is promise and fulfilment. The Old Testament makes hundreds of specific predictions about a coming Messiah — his lineage (from Abraham and David), his birthplace (Bethlehem, Micah 5:2), his entry into Jerusalem on a donkey (Zechariah 9:9), betrayal for thirty pieces of silver (Zechariah 11:12–13), the details of his death (Psalm 22), and his resurrection (Psalm 16:10). The New Testament presents Jesus as the one who fulfils them all.

Jesus himself makes this claim explicitly: "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). On the road to Emmaus after the resurrection, he walks two disciples through the entire Old Testament: "Beginning with Moses and all the Prophets, he explained to them what was said in all the Scriptures concerning himself" (Luke 24:27). The whole OT, he is saying, was pointing to him.

Augustine of Hippo captured this relationship with a phrase that has become classic: "The New Testament is concealed in the Old; the Old Testament is revealed in the New." You cannot fully understand either without the other.

The Change in Covenant: Law and Grace

One of the most common sources of confusion is how the Old Testament law relates to Christians today. Does the dietary law of Leviticus still apply? What about the civil laws given to Israel? Do Christians need to observe the Sabbath on Saturday?

The New Testament's answer is nuanced but clear. The Mosaic Covenant was a specific, time-bound covenant between God and the nation of Israel. It had three types of law: moral law (the Ten Commandments and their extensions), ceremonial law (sacrifices, dietary rules, festivals), and civil law (governing Israel as a theocratic nation). The New Testament teaches that Christ's death fulfilled the ceremonial law — he is the final sacrifice to which all the animal offerings pointed (Hebrews 10:1–14). The civil law applied to Israel as a political entity, not to the universal church. The moral law — rooted in God's unchanging character — remains binding, now written on the heart rather than on stone tablets (Jeremiah 31:33, Romans 2:15).

Hebrews 8:13 states it plainly: "By calling this covenant 'new,' he has made the first one obsolete; and what is obsolete and outdated will soon disappear." The new covenant, inaugurated by Jesus at the Last Supper ("This cup is the new covenant in my blood," Luke 22:20), does not contradict the old — it fulfils and supersedes it.

The God of Both Testaments

A very old heresy — Marcionism, dating to the 2nd century — claimed that the God of the Old Testament (harsh, judgemental, full of wrath) is different from the God of the New Testament (loving, gracious, merciful). This misreads both Testaments.

The Old Testament God is the one who said "I have loved you with an everlasting love" (Jeremiah 31:3), who is "compassionate and gracious, slow to anger, abounding in love and faithfulness" (Exodus 34:6), who runs after a wayward people through the imagery of Hosea and makes clothing for naked and ashamed Adam and Eve (Genesis 3:21). The New Testament God is the one who judges sin at the cross, who will throw death and Hades into the lake of fire (Revelation 20:14), whose wrath is revealed from heaven against wickedness (Romans 1:18). Both attributes — holiness and love — run through both Testaments, because it is the same God throughout.

What changes between the Testaments is not God's character but the stage of his redemptive plan. The Old Testament operates in shadow and type — the sacrificial system, the priesthood, the temple — anticipating a reality that has not yet arrived. The New Testament operates in the light of fulfilment: "The Son is the radiance of God's glory and the exact representation of his being" (Hebrews 1:3). The picture comes into focus.

Practical Differences for Readers

When reading the Bible, a few practical differences are worth keeping in mind:

Audience and application. The commands in Leviticus are addressed to Israel as a covenant nation. The commands in the New Testament letters are addressed to the church — Jews and Gentiles united in Christ. Both are Scripture and profitable for teaching (2 Timothy 3:16), but their direct application differs. A Christian is not obligated to offer animal sacrifices; the book of Hebrews explains at length why.

Progressive revelation. God did not reveal everything at once. The full doctrine of the Trinity, for example, is implicit in the Old Testament but explicit in the New. The nature of life after death is clearer in the NT. The scope of God's purposes — extending to all nations, not just Israel — is hinted at throughout the OT (Genesis 12:3, Isaiah 49:6) but announced fully in the NT.

Both are equally Scripture. The New Testament does not replace or invalidate the Old. Paul says "All Scripture is God-breathed and useful" (2 Timothy 3:16) — and when he wrote that, "Scripture" meant the Old Testament. Jesus quotes from the Law, the Psalms, and the Prophets constantly. The OT is not the rough draft that the NT corrects; it is Act One of a story whose Act Two cannot be understood without it.

"For everything that was written in the past was written to teach us, so that through the endurance taught in the Scriptures and the encouragement they provide we might have hope." — Romans 15:4 (NIV)

For further reading, GotQuestions.org's article "What is the relationship between the Old and New Testaments?" is thorough. Graeme Goldsworthy's Gospel and Kingdom (Paternoster, 1981) is the best short introduction to reading the OT in light of Christ. Alec Motyer's Look to the Rock (IVP, 1996) explores the OT's witness to Christ in depth.