The apostles had received a unique mission of witness, but their gradual disappearance under the effect of persecution made it necessary to preserve their teaching in writing.
First, the Twelve had been chosen to be eyewitnesses of the life, death and resurrection of the Messiah Jesus (Acts 1.21-22). Their authority rested on what they had seen and heard (John 15.27; 1 John 1.1-3). Peter would later recall:
“For we did not follow cleverly devised fables when we made known to you the power and coming of our Lord Jesus Christ, but we were eyewitnesses of his majesty” (2 Peter 1.16).
The apostles therefore constituted the historical foundation of the Church. Paul would write that it is:
“built on the foundation of the apostles and prophets, Christ Jesus himself being the ” (Ephesians 2.20).
However, this group was particularly vulnerable. From the earliest years, James, son of Zebedee, was put to death under Herod Agrippa I (Acts 12.1-2). Peter was imprisoned several times (Acts 5.18; Acts 12.3-5), while Paul suffered persecution, imprisonment and finally martyrdom (2 Timothy 4.6-8). The direct witnesses of Jesus' ministry were destined to disappear.
This situation probably explains the gradual appearance of the writings of the New Testament. Luke stresses from the introduction of his Gospel that many had undertaken to put in writing the events handed down by “those who from the beginning were eyewitnesses” (Luke 1.1-2). John also states the reason for his work:
“But these are written so that you may believe that Jesus is the Christ, the Son of God” (John 20.31).
Peter himself seems aware of his approaching death and expresses the wish that believers may keep his teaching after his departure:
“I will make every effort so that after my departure you may always be able to remember these things” (2 Peter 1.13-15).
It is hard not to see in this statement an allusion to the need for a lasting testimony, independent of the physical survival of the apostles.
Thus the Church gradually moved from an essentially oral tradition, carried by living witnesses, to a written tradition intended to preserve their testimony faithfully. The Gospels and the epistles appear as the natural heirs of this apostolic mission. As the witnesses passed away, their writings became the preferred means of handing on the faith to the following generations.
The Church Fathers of the second and third centuries were fully aware of this continuity. Irenaeus of Lyon affirmed that the apostles had first preached orally, then handed down in writing what was to become the foundation of the Christian faith. For his part, Eusebius of Caesarea reports that the disciples of the apostles felt the need to preserve their testimony in writing when the apostles began to disappear.
One may thus consider that the books of the New Testament represent, in a way, the extension of the apostolic testimony. Men were mortal and exposed to persecution, but their testimony was to remain until the end of time (Matthew 24.35). That is why, after the apostles passed away, the Church no longer sought to recreate a new college of the Twelve: it turned to their written legacy, regarded as normative and sufficient for the teaching, correction and training of believers (2 Timothy 3.16-17).