What does Philemon 1:8 mean?

The New Testament refers to all Christian as "saints" (Philemon 1:7). Paul also refers to the believers in Colossae as "saints" four times in Colossians chapter 1 (Colossians 1:2–4, 12, 26).

Verse 8 shifts Paul's focus to Onesimus, Philemon's runaway slave. Rather than start with Philemon's authority over his slave, Paul begins with his own authority. Paul not only has a mandate given to him by God as an apostle, he also has the boldness to use it, when appropriate. Paul could have directly commanded Philemon to forgive and release Onesimus. However, as the following verses show, Paul's preference is to appeal to Philemon's positive qualities, mentioned in verses 4–7.

Paul's reference to doing "what is proper," or "what is required," is a general statement, yet Paul has something specific in mind. In verse 13 he will express willingness to keep Onesimus with him, to serve Paul in prison on Philemon's behalf. Paul will also ask Philemon to receive Onesimus the same way he would receive Paul (Philemon 1:17). This means treating him as an honored guest (Philemon 1:22), and as a brother (Philemon 1:16).

Putting these together implies that Paul wants Philemon to forgive his runaway slave, and then free him from slavery, so he can serve in ministry. This was a remarkably bold request in that culture. It would require a large expression of the love Paul had just praised Philemon for having towards all the saints (Philemon 1:7).