Paul, with great diffidence, approaches the request he is about to make. I would like to keep him, or perhaps better in English, “I would have liked to keep him,” indicates his personal preference in the matter, which he is forgoing in view of the fact that by right the decision about Onesimus’ future belongs to Philemon, not to Paul. (For similar use of eboulomēn see Acts 25.22.)
I would like to keep him here with me suggests something that Paul would not do, and therefore it may be necessary to make this fact explicit, for example, “I would like to keep him here with me but I will not do so.” To keep him here with me may be rendered as a causative, for example, “I would like to cause him to remain with me.”
There is a rather awkward relationship between clauses in verse 13, for people could understand the purpose clause so that he could help me in your place as being related to while I am in prison for the gospel’s sake. Obviously, however, the clause so that he could help me in your place goes with I would like to keep him here with me. It may, therefore, be preferable to place the temporal clause at the beginning of verse 13, for example, “while I am in prison for the gospel’s sake, I would like to keep him here with me so that he can help me in your place.”
He could help (Good News Translation) or “he might serve” (Revised Standard Version) translates the subjunctive of the verb diakoneō. The general meaning “to help” is preferable, since Paul speaks of Onesimus’ doing this in Philemon’s place; “serve” might be understood to refer to rather menial or degrading work in prison.
In your place: Paul is saying that Onesimus would be doing what Philemon would have been glad to do (see especially Barclay). It is frequently necessary to make the relationships indicated in the phrase in your place somewhat more specific. For example, the last clause of verse 13 may be rendered as “so that he could help me by doing what you would do if you were here.”
In prison for the gospel’s sake: Paul does not specify the occasion of being arrested and jailed because of his activities as an apostle. The words may be translated as “in prison because of having announced the good news,” or “… because I preached the good news,” or “because of my faithfulness to the good news.”
Quoted with permission from Bratcher, Robert G. and Nida, Eugene A. A Handbook on Paul’s Letter to Philemon. (UBS Handbook Series). New York: UBS, 1977. For this and other handbooks for translators see here .