Any survey of the history of the church of Jesus Christ in its first few centuries will reveal that the New Testament canon developed over time. For example, it is obvious from reading the book of Acts that the apostles were not spreading their message about Jesus by passing out New Testaments. On the contrary, their proclamations were constantly appealing to what we call the Old Testament. Not until the 4th Century can scholars find a list of 27 writings upon which they can agree matches what we have in the table of contents in our New Testament. Since that time, the canon has been closed and its contents stable. Thus, though the New Testament canon has been settled for 16 centuries, it took several centuries to become so. (See also Chronology of the New Testament Text and Canon.)
“What is really remarkable…is that, though the fringes of the New Testament canon remained unsettled for centuries, a high degree of unanimity concerning the greater part of the New Testament was attained within the first two centuries among the very diverse and scattered congregations not only throughout the Mediterranean world but also over an area extending from Britain to Mesopotamia.” – Bruce M. Metzger, The Canon of the New Testament: Its Origin, Development, and Significance, page 254.
We see in the New Testament (i.e. the 1st Century) that Paul’s letters were accorded a certain status by the apostles themselves (1 Thessalonians 5:27; Colossians 4:16; 2 Peter 3:15-16). Early in the 2nd Century we begin to see that the Gospels were circulating with the same sort of status. Over the next century or two, other documents were deemed to be apostolic by more and more churches such that these additional documents were added to Paul’s letters and the Gospels as worthy of the same status. Finally, we see Athanasius bear witness to a commonly-accepted and closed canon in the 4th Century (see also Chronology of the New Testament Text and Canon).
Like leaven that works its way into the whole lump, all 27 writings were eventually accepted by the worldwide church. Just because the boundaries of the canon weren’t firmly established in the 1st through 3rd centuries does not mean that there was no canon at all in that time period. The canon began as a seed and developed into a tree – over time. By the 4th Century, the edges of the canon had been fully trimmed and it was time for the ancient church to close its canon. We can accept their witness or reject it…but we cannot change it.
Most importantly, since canonicity equates to apostolicity insofar as the New Testament is concerned, by the firming of the borders of the canon in its time, the ancient church has identified for us the writings they deem to have come from the apostles. Do we think we know better than they?