This post is an extremely brief introduction to reading the letters of the New Testament. There is much that could be written about this subject. Our goal today is to offer some  basic information to aid your reading.
In the New Testament letters are sorted into two groups, letters historically attributed to Paul and letters by others (John and Peter, sometimes called the catholic epistles or letters). The letters attributed to Paul  are arranged first as letters addressed to churches (longest to shortest) and  then letters addressed to individuals (again longest to shortest).  The Letter to the Hebrews, whose authorship is unknown, is located between the letters of Paul and the catholic letters.
Letters in the Roman World
Sometimes the letter writer wrote their letter, sometimes they dictated their letter to a scribe. Dictation could be word for word, but sometimes the ideas and content were dictated and the scribe chose the words used. The literacy rate in the first century AD was between 10-15% and because of the low literacy rate, letters were written to be read out loud. The people of the early church lived in an oral culture and were used to listening.
Scholars tell us there were many styles of letter writing in the ancient world. People were familiar with the different styles and expected letters to adhere to letter writing conventions. It was a culture that valued letters and the art of letter writing. But this didn’t mean it was simple or easy to send and receive letters.
There was no postal service for private letters. Letters were sent by couriers (Rom 16:1; 1 Cor 16:10; 1 Peter 5:17). As you can imagine, in the first century travel was hazardous and seasonal. Illness, accidents, bandits, bad weather and just plain bad luck all affected the delivery of letters. Scholars think that couriers were sometimes more than simply delivery agents. Couriers may also have had information to share with the recipients that was not contained in the letter (Eph 6:21-22; Col 4:7-9).

In the New Testament
The letters we have in the New Testament are one side of a conversation. We don’t know with documented certainty what questions, concerns or situations Paul ( or Peter or John) were responding to in their letters. Scholars have well- researched ideas that are a great help in our understanding of the letters, but we do not have the letter or conversation that caused Paul, Peter or John to write.

We do know the letter writers were writing to particular congregations and individuals about particular issues and concerns. The original purpose of these letters are pastoral. The letters of the New Testament are not exercises in systematic theology removed from the actual situations of real people. They are written to particular congregations and individuals about particular concerns or situations.
Paul’s letters are carefully crafted and he uses different styles and rhetorical practices in different letters. His letters do have a common structure that is consistent with ancient letter writing conventions.
Opening: Here we find the name of the sender(s), the name of the recipients, a greeting and (with one exception) a prayer of thanksgiving for the recipients.

Closing: There is variety in how Paul closes his letters. There are greetings to and from friends, a benediction, sometimes a prayer, and there are final admonitions and instructions.

Body: Here there is much variety. Often “brothers and sisters” opens the body of the letter, along with a statement such as “I want you to know…” or “ We do not want you to be unaware…” or I appeal to you…” .  Often at the end  of the body is a moral exhortation to the reader. Sometimes these are lists of vices or virtues or a series of maxims.

 A word (or two) about authorship 
     There are some letters attributed to Paul, that scholars believe with great certainty were written by Paul. There are other letters whose authorship is less certain but historically have been attributed to Paul. Today, we consider it bad form (even illegal) to write something and attribute it to someone else. Sometimes documents were written to deceive, but not necessarily.  In ancient times followers of teacher might write something in the tradition of the teacher and attribute it to the teacher. This was a way to honor the teacher and acknowledge the teacher’s influence.
Reading Tip 
     Because the letters of the New Testament were meant to be read aloud, reading them aloud can greatly help our understanding and appreciation of them. Don’t be afraid to give it a try.
Read More About It:
Cousar, Charles B.; “Introduction to Books in the Form of Letters” ; HarperCollins Bible Commentary, James L. Mays, ed., The Society of Biblical Literature, HarperSanFrancisco, 2000.

Johnson, Luke Timothy, The Writings of the New Testament: An Interpretation, Revised Edition. Augsburg Fortress Press: 1999, 261-273.

Metzger, Bruce M., “Letters/Epistles in the New Testament” ,The New Oxford Annotated Bible with the Apocryphal/Deuterocanonical Books. NRSV. Bruce M. Metzger, Roland E. Murphy, eds. Oxford University Press:1994.

Wall, Robert, W. “Introduction to Epistolary Literature” ; New Interpreter’ Bible, Volume X, Leander E. Keck, ed. Abingdom Press, 2002.