Whom I was desirous to keep beside me. This is another argument for the purpose of appeasing Philemon, that Paul sends him back a slave, of whose services, in other respects, he stood greatly in need. It would have been extreme cruelty, to disdain so strong affection manifested by Paul. He likewise states indirectly, that it will be a gratification to himself to have Onesimus sent back to him rather than that he should be harshly treated at home. That he might minister to me instead of thee in the bonds of the gospel. He now mentions other circumstances: first, Onesimus will supply the place of his master, by performing this service; secondly, Paul himself, through modesty, was unwilling to deprive Philemon of his right; and, thirdly, Philemon will receive more applause, if, after having had his slave restored to him, he shall willingly and generously send him back. From this last consideration we infer, that we ought to aid the martyrs of Christ by every kind office in our power, while they are laboring for the testimony of the gospel; for if exile, imprisonment stripes, blows, and violent seizing of our property, are believed by us to belong to the gospel, as Paul here calls them, whoever refuses to share and partake of them separates himself even from Christ. Undoubtedly the defense of the gospel belongs alike to all. Accordingly, he who endures persecution, for the sake of the gospel, ought not to be regarded as a private individual, but as one who publicly represents the whole Church. Hence it follows, that all believers ought to be united in taking care of it, so that they may not, as is frequently done, leave the gospel to be defended in the person of one man.

Whom I would have retained with me, that in thy stead - "That he might render me the service which I know you would if you were here." The Greek is: "for thee" ὑπὲρ σοῦ huper sou; that is, what he should do for Paul might be regarded as done by Philemon himself.
He might have ministered unto me - He might have rendered me assistance (διακονῇ diakonē); to wit, in such a way as one who was in bonds would need.

That in thy stead he might have ministered unto me - As Philemon was one of Paul's converts, he became thereby his spiritual father, and had a right to his services when in need. This was a strong argument, not only to induce Philemon to forgive his servant, but to send him back to the apostle, that he might minister to him in his master's stead.

Whom I would have retained with me,.... At Rome, where the apostle was a prisoner:
that in thy stead he might have ministered unto me in the bonds of the Gospel; the apostle was in bonds, not for any crime, for any immorality he had been guilty of, but for the sake of the Gospel, for professing and preaching that; for this he was an ambassador in bonds, as he elsewhere says, Ephesians 6:20. Now he would have kept Onesimus with him, either to have waited upon him, in his bonds, and to have provided for him the necessaries of life; or to have assisted him in the ministration of the word, in the room of Philemon, who, had he been there, would have been employed in such service; so that if the apostle had retained him, he would have been acting not for himself, but in the room of his master, and doing what he should have done, had he been on the spot. This the apostle observes to prevent an objection that might have been made; that since Onesimus was become so profitable to him, why did he send him back? why did he not keep him for his own service? this he obviates and removes, by signifying he should have done it, but for the following reason.

I--emphatical. I for my part. Since I had such implicit trust in him as to desire to keep him with me for his services, thou mayest.
I would have retained--different Greek from the "would," Plm 1:14, "I could have wished," "I was minded" here; but "I was not willing," Plm 1:14.
in thy stead--that he might supply in your place all the services to me which you, if you were here, would render in virtue of the love you bear to me (Plm 1:19).
bonds of the gospel--my bonds endured for the Gospel's sake (Plm 1:9).

To serve me in thy stead - To do those services for me which thou, if present, wouldest gladly have done thyself.