This is a subsidiary post of The Formation of the New Testament…from Beginning to End.
Although we can see New Testament documents being considered authoritative even in New Testament days (i.e. the first century), it is not until the fourth century that we find evidence acknowledging the 27-book New Testament that we know today. Why so long?
For one thing, there are no instructions in the New Testament to assemble a New Testament. Jesus did not command, “Assemble the writings of My apostles, call it “the New Testament,’ and then combine it with the Scriptures I have followed, which you can now call ‘the Old Testament,” and call the combined collection ‘the Bible’.” There were many things that Jesus did command, but the production of a set of writings to be called the New Testament was not among them.
Instead of commanding that a New Testament be produced, God worked patiently through stubborn and obstinate people to assemble the literary remains of the apostolic mission into a cohesive and effective textual witness to Himself. Like He secretly forms a human being in the womb of a woman, so He formed the New Testament…and it is a marvel to our eyes (Psalm 118:23).
The church was instrumental in the formation of the New Testament just as Israel was instrumental in the formation of the Old Testament. In neither case were the instruments always and fully aware of their role in the process. Neither were the instruments always righteous in the execution of their roles. On the contrary, consider the scribes who assembled the Old Testament and presented it to Jesus. Their hearts were hard and they did not know the Lord who had given them the Scriptures to which they professed allegiance so loudly.
It took about 400 years from the time the 27 New Testament writings were individually written for them to be solidified into a literary unit – no writing to be removed, no writing to be added. It is not the only time God has taken that long to do something. He spent four hundred years with Israel in the land of Egypt, preparing them for deliverance (Acts 7:6). It was another 480 years after that before King Solomon would lay the foundation of the temple in Jerusalem (1 Kings 6:1). The time from Ezra, Nehemiah, Zechariah, and Malachi to the birth of Messiah was 400-500 years. Thus we should not be surprised if God should take longer than a human lifetime to do something important.
It not as though the world was without a witness to Christ during that formative period. On the contrary, the oral tradition about Christ would have been widely available during that time. You can find more on this in The Factors Involved in New Testament Formation.
Consider also that the majority of the New Testament writings (that is, the Gospels, Acts, and the letters of Paul) were circulating throughout the Mediterranean world in the second, and even the first, centuries. Though the other New Testament writings may not have been circulating as widely at that time, it is not as though they were not available to anyone. So even though the New Testament was not circulating as a 27-book collection in the first and second centuries, it does not mean that people were unaware of its contents.
Given the way that Israel’s prophets were treated during their lifetimes, it is hard to imagine that their writings were treasured during their lifetimes. Yet eventually their writings were treasured in the temple along with those of Moses. How much more then would the apostles’ writings have eventually made their way into a unified collection along with those of the prophets – if only enough time could pass for this to take place (Matthew 23:29-31).