How do we know which books belong in the Bible?

This is one of the most important questions about Scripture, and it deserves a careful answer because it is often used to suggest that the biblical canon is arbitrary — that the church just picked the books it liked and excluded the rest.

The process of canon formation was neither arbitrary nor purely political. The criteria the early church used to recognise canonical books were: apostolic origin or connection (written by an apostle or someone with direct apostolic oversight), consistency with the rule of faith already established, and universal or near-universal acceptance across the churches.

The New Testament canon was not decided at the Council of Nicaea in AD 325 — a claim that circulates widely and is historically false. Nicaea dealt with the deity of Christ, not the canon. The canon was formally recognised at councils like Carthage (AD 397), but the books recognised there were those already widely accepted by the churches for generations. The council did not create the canon — it acknowledged what the church had already received.

The books that were genuinely disputed — like Hebrews, James, 2 Peter, and Revelation — were disputed precisely because their apostolic origins were questioned by some, not because of their content. The books that were decisively rejected — the Gnostic gospels, the Gospel of Thomas, and others — were rejected because they were late (second century or later), of dubious origin, and often theologically inconsistent with the apostolic deposit.

The Old Testament canon was largely settled for Jesus and the first-century Jews. Jesus and the apostles quoted from the Hebrew Scriptures consistently, and their quotations align with what we now call the Protestant Old Testament. The deuterocanonical books (accepted in Catholic and Orthodox Bibles) were included in the Greek Septuagint but were not universally accepted by first-century Judaism or the early church.

The canon we have is not the result of human power games. It is the result of the church recognising, over time, which books bore the marks of divine origin and apostolic authority.