Text below is from Bart D.Ehrman in Misquoting Jesus
The Story Behind Who Changed the Bible and Why p.21,22
A Purpose of Teaching & Converting
"The earliest evidence we have for Christian communities comes from letters that Christian leaders wrote.
The apostle Paul is our earliest and best example.
Paul established churches throughout the eastern Mediterranean, principally in urban centers,
evidently by convincing pagans that the Jewish God was the only one to be worshiped, and that Jesus was his Son,
who had died for the sins of the world and was returning[?] soon for judgment on the earth
(see 1 Thess. 1:9-10).
...
After Paul had converted a number of people in a given locale,
he would move to another and try, usually with some success,
to convert people there as well.
But he would sometimes (often?) hear news from one of the other communities of believers
he had earlier established, and sometimes (often?) the news would not be good:
members of the community had started to behave badly, problems of immorality had arisen,
"false teachers" had arrived teaching notions contrary to his own,
some of the community members had started to hold to false doctrines, and so on.
Upon hearing the news, Paul would write a letter back to the community, dealing with the problems.
That Became Scriptures
These letters were very important to the lives of the community, and a number of them eventually came
to be regarded as scripture. Some thirteen letters written in Paul's
name are included in the New Testament.
We can get a sense of how important these letters were at the earliest stages of the Christian movement
from the very first Christian writing we have, Paul's first letter to the Thessalonians,
usually dated to about 49 C.E., some twenty years after Jesus's death and some twenty years before
any of the Gospel accounts of his life.
Paul ends the letter by saying,
"Greet all the brothers and sisters with a holy kiss;
I strongly adjure you in the name of the Lord that you have this letter read to all the brothers and sisters"
1 Thess. 5:26-27
This was not a casual letter to be read simply by anyone who was mildly interested;
the apostle insists that it be read,
and that it be accepted as an authoritative statement by him, the founder of the community.
Letters thus circulated throughout the Christian communities from the earliest of times.
These letters
- bound together communities that lived in different places;
- unified the faith and the practices of the Christians;
- indicated what the Christians were supposed to believe and how they were supposed to behave.
They were to be read aloud to the community at community gatherings-since, as I pointed out,
most Christians, like most others, would not have been able to read the letters themselves.
A number of these letters came to be included in the New Testament.
In fact, the New Testament is largely made up of letters written by Paul and other Christian leaders
to Christian communities (e.g., the Corinthians, the Galatians) and individuals (e.g., Philemon).
Moreover, the letters that survive, there are twenty-one in the New Testament are only a fraction of those written.
...
Scholars have long suspected that some of the letters found in the New Testament under Paul's name
were in fact written by his later followers, pseudonymously.
If this suspicion is correct [and it is],
it would provide even more evidence of the importance of letters
in the early Christian movement: in order to get one's views heard, one would write a letter in the apostle's name,
on the assumption that this would carry a good deal of authority.
...
The various Christian communities, unified by this common literature that was being shared back and forth
were adhering to instructions found in written documents or "books."
"And when this letter has been read among you, have it also read in the church of the Laodiceans; and see that you also read the letter from Laodicea."
Colossians 4:16