The most likely candidate for the job of "first interpreter" of Paul's letters is probably the person who delivered it. Whoever it was that delivered the letters to Corinth or Galatia was probably very familiar with the situation and prepared to provide answers and explanations in the absent apostle's stead. This is probably what happened with Timothy in Thessalonica (1 Thess 3:2) and Phoebe in Rome (Rom 16:1).
In a recent paper delivered at the New Testament Seminar at Cambridge University Peter Head examined Paul's letter to Philemon and wondered who carried the letter. Here is some of what Peter had to say as reported by Peter Malik at RBECS.
In order to interpret the role of the letter-carrier in Philemon, Peter Head first of all presented relevant parallels found in three corpora of ancient epistolary material, namely the Oxyrhynchus papyri, the ancient Jewish epistolary material, and the letters of Cicero. The reason why these three were chosen is they all are in a sense ‘bounded’ groups of literature, and are diverse enough to extrapolate general characteristics applicable to the ancient epistolography. Head demonstrated that one can glean several common characteristics of the named letter-carriers in antiquity: (1) the letter-carriers were present at the composition of the letter; (2) they, obviously, delivered the letter; (3) and, finally, they were present at its reading. Many letters at Oxyrhynchus indicate that the named letter-carrier mediated to the recipient the fuller information that was only partly present in the letter, especially so in the letters of recommendation. Similarly, in Jewish epistolography, one often finds that the named letter-carrier was to reinforce and supplement the overall argument of the letter. The letter-carriers in Ciceronian texts display a wider array of functions, depending on Cicero’s purpose in a given letter, but the above mentioned characteristics are strongly present in his letters as well.
How does all of this come together in Philemon? Our presenter argued that it’s precisely the role of the letter-carrier, which plays a decisive role in the interpretation of this ambiguous, highly problematic little letter. Having established that Philemon is best categorised as ‘the letter of recommendation’, Head also alluded to John Barclay’s hypothesis that Paul’s ambiguity was probably occasioned by the difficulty Paul was facing in this precarious situation; indeed, Paul could do, by way of letter, little more, and thus the practical implications weren’t spelled out clearly in writing. This is precisely the point where Head’s research into the ancient letter-carrier makes a decisive move: Paul’s confidence in his letter-carrier implies that, in the light of the ancient parallels, Onesimus was entrusted to deliver and interpret the message addressed to Philemon. What would then Paul have Onesimus say to Philemon? In short, Dr. Head intimated that Paul would request Philemon that Onesimus be released, forgiven, and sent back to Paul. Firstly, Dr. Head pointed out that in 1 Cor 7, Paul intimates that the slaves who can become freedmen, should ‘avail themselves of the opportunity.’ This reflects the generally shared sentiment in antiquity–the slaves, above all, desired freedom. Therefore, there’s no reason to think that Onesimus would have felt otherwise. Thus, Onesimus’ role as the letter-carrier of Paul’s epistle to Philemon is of principal importance for resolving some of its, otherwise obscured, ambiguities.
You can read the whole review of the paper here.
I like what Pete has to say here. I have wondered what it must be like for Onesimus to stand there, perhaps a bit nervous with a slight sweat, as his master read the letter. Considering the way that Paul describes Onesimus in the letter and the way that Paul paints Philemon into a corner, it seems quite plausible that Onesimus was not only the subject of, but also the deliverer of the letter.
If you are interested in learning more about interpreting Philemon and the situation of Onesimus you can check out the following essay I published: “The Epistle to Philemon: Paul’s strategy for forging the ties of kinship” pp.205-216 in Jesus and Paul: GlobalPerspectives in Honor of James D.G. Dunn for his 70th Birthday. (LNTS; T& T Clark, 2009).
Here is a link where you can read/download the essay online.