For this post, it will help if you read someone else's mail; specifically Paul's letter to Philemon:
The inclusion of the letter of Philemon in the canon of scripture, is somewhat fortunate, I think. Unlike a lot of Paul's letter where he is unravelling great doctrinal truths in rolling paragraphs, the letter to Philemon is reasonably short and concise. It is so short in fact, that even in the twenty-first century where we have the attention span of a cat, that we're still capable of composing longer correspondence if the need arises. The whole of the letter is less than 500 words long.
The problem posed is reasonably straightforward enough. Philemon owns a slave name Onesimus who has apparently run away; has somehow met up with Paul and in the process become a Christian, and now Paul is sending Onesimus back to Philemon with an appeal for forgiveness and hopefully reconciliation.
As someone from the twenty-first century, there is one thing which is culturally strange to me. That is, that Philemon who has a church which meets in his house, doesn't appear to have a internal conflict in owning slaves. Admittedly, slave ownership was a somewhat common thing even up to the nineteenth century (and famously the United States went to war against itself over that issue amongst others) but that still strikes me as being odd.
The reasons why Onesimus came to meet Paul are entirely unclear from the text of the letter. Maybe Onesimus ran away because he was being treated badly, maybe Onesimus had done something terrible and was sent away and just happened to come into contact with Paul, maybe there was some project like a building construction which Onesimus was jobbing on and he and Paul just happened to have met - we just don't know. Not even Paul's appeal in the text is clear about the nature of the injury in the slave-master relationship, or if any actual debt has been incurred.
What is apparent from the text is that Paul is sending Onesimus back to Philemon and is appealing for forgiveness and or the rebuilding of a relationship despite uncertain circumstances. Evidently, Paul and Philemon are on cordial terms because Paul requests that Philemon prepares a guest house for him, in preparation of an impending visit. We can't know from the text whether this was in answer to some request, or whether Paul intends to check up on Philemon to make sure that he's looking out for Onesimus' welfare because again this is unclear from the actual words of the text.
Its obvious in scripture that Paul wrote far more letters than what happened to fall through the cracks of history and are preserved for us. The most famous of these is probably the "tearful" letter to the Corinthians but there are others. Philemon is interesting because its continued survival through those cracks of history, isn't necessarily what you would expect if it was your intention to build a canon of scripture for a new religion. I can't think of any other set of religious canon which includes a letter dealing with the subject of labour relations.
What this says to me is that one of the big differences between the fledgling Christianity as opposed to the existing religions of Judaism or Greco-Roman Pantheism was that Christians saw their relationship with God, as something which should form the model in looking at relationships with each other.
The story of the problem of Onesimus as either a runaway or as a nefarious bad man, would still have the same broad solution; that is one of reconciliation and forgiveness. The parallel between us and God is obvious; indeed the very message of the gospel itself revolves around those issues of reconciliation and forgiveness.
Indeed it is also worth noting that Roman Law allowed a slave owner an almost unlimited ability to exact punishment on slaves for transgressions; including execution if they had run away (though I fail to see what good that would have achieved).
Paul's offer to pay back what ever Onesimus owes Philemon is also an admission that sometimes reconciliation and forgiveness comes with associated costs; this is a mirror of the fact that in dealing with the costs incurred for the charges of sin, Christ paid those charges with his own death and resurrection.
What would have been absolutely shocking and perhaps even downright scandalous to a first century reader of the letter to Philemon (and maybe for readers of the next eighteen centuries as well) is that Paul's prime concern isn't perhaps for Philemon but the dignity of his slave Onesimus. This must rest on the premise that not only does a slave have an intrinsic value as a person rather than a piece of chattel to be traded but that they are due a certain amount of dignity in their own right. Whilst that doesn't seem particularly odd to us, bear in mind that at the time of writing, there may have been as many as five million slaves across the Roman Empire or about 15% of the total population.
In this light even admitting that slaves have intrinsic dignity, is to put up a challenge to the very fabric of society itself especially considering that the person writing this, Paul, is a Roman citizen.
It's pretty well much safe to assume that this letter was written in the late 50's or early 60's and I think that it's also possible that this letter could have been sent along with Tychicus and Onesimus, with the letter to the church at Colossae (because they are both mention in Colossians 4:7-8) and also with a letter to the church at Laodicea (which hasn't survived).
History doesn't record what happened to either Onesimus or Philemon but tradition says that Onesimus became a leader at the church in Ephesus. I don't know if that can be verified. Certainly Onesimus isn't mentioned in the letter to church in Ephesus which was probably written about four or five years later than the letter to Philemon, though it is curious that Paul used the same courier Tychicus.
What we can take away from this though is that Paul thought that forgiveness and reconciliation were a worthy aim; even if it was going to cost him personally. That's worth thinking about, in all circumstances.
So if you consider me a partner, welcome him as you would welcome me. If he has done you any wrong or owes you anything, charge it to me.