In the second and third centuries following the death of the Lord Jesus Christ, an intellectual movement known as Gnostics began plagiarizing the New Testament documents, mixing neo-paganism with Christianity. The Gnostics created an ingenious, yet insidious, writing campaign introducing religious papers that took on a christian form.
These “gospels” deviated in substance from what had previously been well known and reputed as the official apostolic letters written three centuries prior to Gnostics arriving on the scene. In response to the Gnostic heresy, and to help new Christians who were confused over the matter (much as they are today), church leaders officially declared the documents which were already widespread and generally accepted as authoritative apostolic letters as “The Bible.”
We know that the entire civilized world had heard authentic Christian preaching almost immediately following the death and Resurrection of the Lord Jesus Christ because there are well preserved records drafted by Roman authorities and first-century historians indicating so (Josephus, Thallus, Phlegon, Pliny, Tacitus, Hadrian, Suetonius, Lucian of Samosata, etc.). Furthermore, we have numerous sermons of early Christian scholars commenting on the various letters of what we now call the New Testament. In an early instance, Clement of Rome (circa A.D. 95) wrote to the Christians in Corinth using renderings of material from Matthew and Mark’s Gospels.
Considering the frequency and abundance of Scripture cited in early preachers’ sermons, I suppose the greater part of a New Testament Bible could be reconstructed by excerpting the references from all of these sermons if one wanted to take time to do so. In fact, it is significant that the title “New Testament” is actually used and appears in a sermon opposing false teachers as early as 190 A.D., so we know that early on Christians had collected the Apostle’s works and were preaching from them using the same label we do in our own time. Moreover, the letters of the apostles contain repeated exhortations for public reading and there is no reason to believe that first century Christians did not follow these instructions (1 Thes. 5:27; Col. 4:16; Rev. 1:3). The Gospel was preached and written for all to see throughout the world long before the completion of the Canon.