Onesimus’s name was a Greek word that meant profitable, so he was most likely a Gentile. Jews like Paul (Phil. 3:5) hated Gentiles and called them dogs, but Paul called Onesimus “my son.” The answer to racial tension is getting people saved and helping them to grow in grace!
It is popular in grace circles to say that members of the Body of Christ are not born again, but Paul says he had “begotten” Onesimus (1:10). This is significant in that the purpose of the book of Philemon isn’t to teach grace doctrines, it is to illustrate them, and the new birth is illustrated here.
“Time past” and “but now” (1:11) should make you think of Ephesians 2:11-13. Onesimus was profitable as a servant to Philemon. Remember, his name means profitable. But when he ran away, he became unprofitable. This illustrates how the Gentiles were profitable to God when they brought Him pleasure (Rev.4:11) but became “unprofitable” (Rom. 3:12).
Under Roman Law, Philemon could have Onesimus executed for running away. That illustrates what God could have done with the Gentiles when they became unprofitable servants (Mt.25:30). Instead He was merciful to them (Tit.3:3-5). And Paul is asking Philemon to treat Onesimus as God treated him as a Gentile when he was unprofitable and be merciful. That’s what Christianity is all about!
Ask an unbeliever, or even most Christians, the best way to treat others, and they’ll quote the Golden Rule (Mt.7:12). The Lord was alluding to the old covenant of the Law (Lev. 19:18) and the law was glorious, but new covenant grace exceeds in glory (II Cor. 3:6-9) because it says to treat others as God has already treated you.
The word “again” (1:12) means back, as in Exodus 15:19 and Hebrews 13:20. Paul didn’t have to send Onesimus back to his master twice!
But why would Paul send a slave back to his master? Under the Law you weren’t supposed to do that (Deut. 23:15). If you’re thinking you wouldn’t send a runaway slave back, would you give him the best spot on your land to live (v.16)?
This was high spiritual ground! We know the Gentile nations weren’t doing that, for a runaway slave begged David not to send him back to his master (I Sam. 30:15).
So why did Paul send Onesimus back? He knew we are not under law, but under grace (Rom. 6:15). The book of Philemon doesn’t teach that, it illustrates it.
When Paul instead returned Onesimus, that illustrated another grace doctrine, for Paul was obeying Roman law, and believers today are supposed to obey the laws of our country as well (Titus 3:1).
If you’re thinking we’re supposed to obey the government unless they tell us to do something wrong, and returning a slave to his master is wrong, it’s because you think slavery is evil. We know it isn’t because God allowed His people to own them (Lev. 25:44,45). There were legitimate reasons why people were slaves. If they ran up too much debt, they had to work as slaves to pay it off (II Ki. 4:1). But the slavery that we had in the United States was evil (Exodus 21:16).
When Paul says he “sent” Onesimus (1:12) instead of dragging him, that illustrates a tremendous doctrine of grace. Once Onesimus left Paul behind, he didn’t have to go where Paul sent him. But salvation had made him not care about being a slave (I Cor. 7:21). That illustrates the power of grace
Grace can show you how to not care that you’re in the prison that you are in. What grace? Onesimus learned that there are no slaves in Christ, we are all equal (I Cor. 12:13; Gal. 3:26-28). He focused on seeing himself as God saw him, and stopped focusing on his difficult circumstances. Grace can make you care not about your circumstances as well if you do the same. When Paul tells Philemon to receive Onesimus as his own bowels (1:12), he meant to receive him as Paul’s own biological son (cf. II Sam. 16:11). That illustrates how God receives us as His own Son (Eph. 1:6), and how we should receive one another the same way (Rom. 15:7).