Botha, P.J.J. "Chapter Nine: Letter Writing and Oral Communication: Galatians." Orality and Literacy in Early Christianity. Eugene, OR: Cascade, 2013, 203-221.
A letter in antiquity could have many functions, just as one can today. However, Botha notes that our concept of the letter in a biblical context may tend to obscure some of the purposes intended by the author (Botha 2013, 203). The relationship of the composer to specific situational and cultural context is not always clear, though it is certainly important. The structure of Paul's letters is significant. Botha observes that the overall context is of importance.
Botha again notes the oral compositional context of Paul's letters (Botha 2013, 204). Intelligent discourse and composition is not necessarily based on extensive use of and creation of written documents, reviewed by one's own eyes and written with one's own hand (Botha 2013, 205). The mechanical customs of writing could make learning to read fluently a very challenging task, which would often hinder economic productivity. Though there are suggestions that literacy was higher in Jewish circles, Botha does not find significant investigation of those claims (Botha 2013, 206).
Botha notes that, even though the people in the Hellenistic world may have been familiar with books and writing, they would generally depend on the use of the writing skills of other people (Botha 2013, 207). The letters of Paul would have included collaboration of one or more scribes (possibly including Timothy and Silas), who may have had a significant role in the composition as well (Botha 2013, 208). Among the letters in the Pauline corpus, Botha notes that Galatians stands out by having unspecified authors 1(1:1) and by the strongly personal nature of address with extensive use of the first person singular (Botha 2013, 208). There would be an expectation, regardless, that Paul's work involved other people as well.
Delivery of letters was its own challenge. In general, a wealthy individual could send a messenger, normally briefing that person on the content of a message (Botha 2013, 210). The choice of someone to bear a letter was a matter of considerable importance, as that person would normally bring other details along as well. Though a carrier is not mentioned in Galatians, Botha observes the person chosen would likely not only have delivered the letter, but read it aloud at the destination (Botha 2013, 211). Furthermore, Botha observes that the reading of a letter, a public event, would be done using appropriate tone, gesture, and pacing, as if the composer of the letter were there communicating (Botha 2013, 212). Botha goes on to illustrate the process with statements from ancient sources, describing appropriate reading.
Galatians makes significant statements about Paul's apostolic authority (Botha 2013, 214). Through his letter, his intention is to show himself actually present with the Galatians. His emissary, who brought and read the letter, was to be taken as if Paul were there in person. In the case of Galatians, other teachers with another message had presented their message, which Paul considered to endanger the Galatian Christians (Botha 2013, 215). To counteract this, Paul needed to provide his message with sufficient force and eloquence. The messenger would have been extremely important to achieving the goal. While Paul's doctrine undergirds the letter, the doctrine apart from the forceful delivery would be to little or no avail (Botha 2013, 216). Through a variety of emotional appeals, Paul seeks to turn his Galatian audience back in the direction of the doctrine he has previously delivered to them.