Paul now introduces Onesimus into his letter, yet not first of all as Philemon's slave but as Paul's son. Paul does not tell the story behind this letter; letters are not narratives, even though a letter may imply the story of its occasion (see introduction). So we do not know the details of how Onesimus found Paul in prison, under what circumstances or why; nor do we know how he became a believer.
Why Paul waits this long to mention Onesimus in his letter is yet another matter of speculation. To contend that Paul delays referring to Onesimus because he fears offending Philemon or feels Philemon must first be "buttered up" is unwarranted (see O'Brien 1983:290). Rather, this first mention of Onesimus is part of Paul's rhetorical strategy: repeating his appeal (first made in verse 9) in terms of Onesimus's conversion and transformed character (v. 11) will more effectively persuade Philemon to do what Paul requests. Moreover, Paul's appeal presumes that his relationship with Onesimus will prove decisive in moving Philemon toward a new perception of his slave.
Paul defines his relationship with Onesimus as that of a father and son. While son is often found in Jewish writings as a metaphor for the student of a rabbi, it probably is used here as a metaphor of conversion. Paul uses it with became (gennao), as in the birth of a son. In this way "Paul views the process of bringing Onesimus to spiritual birth in a comprehensive glance" (Harris 1991:261). While considerable affection seems to be implicit in Paul's emphatic reference to Onesimus as my son, Paul's primary purpose is to declare Onesimus a true believer. Further, Onesimus's conversion obligates him to Paul in the very same way Philemon's does: both are Paul's spiritual sons. This will become important when Paul seeks to redefine the nature of Onesimus's relationship to Philemon: as Paul's sons, they are now brothers (see v. 16; so O'Brien 1982:291).
Onesimus's name derives from a root that means "beneficial" (compare v. 20), and his service to an imprisoned Paul is testimony to his name. Onesimus is introduced into the sentence last and in apposition to Paul's reference to his conversion. Thus, his name may well be his new Christian name, indicating his new birth in Christ.
This possibility seems plausible because of the additional statements of verse 11, which extend the importance of Onesimus's name. The idiom "then . . . but now" (pote . . . nyni de) is employed frequently by Paul to introduce the general results of Christ's death and the specific results of conversion. In the case of Onesimus, conversion in Paul's prison cell has resulted in his personal transformation: once he was useless (achrestos) but now he is useful (euchrestos). These two words are frequently contrasted in ancient moral literature and typically refer to a person's character more than to the quality of one's work (O'Brien 1982:291-92). According to Paul, the gospel yields the fruit of virtue; spiritual conversion results in a better person who enjoys transformed relationships with others (see commentary on Col 3:5-11).
This point is deepened by the recognition that the common root of these two words (chrestos) sounds the same as the word for Christ (Christos). Wright argues that Paul uses a pun, as was common in ancient literature, to draw attention to the changes that have taken place in Onesimus now that he is in Christ (1986:182). This pun may have additional value in reminding Philemon and his congregation that Onesimus's personal transformation illustrates the sort of change that Christ's death initiates (see commentary on Col 1:21-23).
Yet Paul is emphatic that the results of Onesimus's transformation benefit not only himself but also Philemon: Onesimus has become useful both to you and to me. What an extraordinary claim! We can surely imagine how Onesimus has been a blessing to the imprisoned Paul in his old age; but it is surprising to learn that the departed Onesimus may be useful to Philemon as well. Paul mentions Philemon first, since he will no doubt want to see for himself the dramatic change that has taken place in Onesimus before he grants Paul's request (so Lohse 1971:201). In any case, the point is rhetorical: Paul's surprising assertion provides the focal point for the next part of his appeal. The practical reason Philemon should agree to Paul's request has now been introduced: because Onesimus is useful to you too.