After all the introductory stuff, Paul gets the heart of the matter – a run-a-way slave named Onesimus. We do not know much of the story, only that Onesimus had been owned by Philemon, had run away, and somehow got connected to Paul. He had become a Christian, and was very helpful to Paul in his ministry. Yet there was a problem – his past.
Onesimus was a run-a-way slave. He was with Paul illegally. He knew he needed to do the right thing. He knew he needed to return to his owner. This letter was sent by Paul to Philemon on Onesimus’ behalf, asking Philemon to consider Onesimus as more than a slave, but now as a brother.
Our Christian liberty does not free us from making things right from our past mistakes. It frees us from the requirement of having to do that, but it does not free us from our responsibility. We are called to do the right thing, even if that right thing is very difficult. We have been freed by God’s grace to do that right thing.