“May I receive from you what I ask” is not a literal translation of the Greek text, but a paraphrase expressing the thought contained in it.
In Greek there stands an expression meaning to receive benefit from something, and then to rejoice in something, or to be gladdened by something.
The Apostle’s speech is either optative or conditional. The thought is this: yes, brother, do this; receive Onesimus.
I would wish to receive benefit from you in this very way, since you owe me even your own self.
Or else: if you do this, I myself would receive benefit from you, would be profited by you, comforted and gladdened by you.
Oecumenius writes: “May I enjoy, or, in that case, I would enjoy your good works in the Lord, or your corrections.”
Theophylact adds: “May I enjoy your benefactions, not in worldly things, but in those things that are in the Lord.”
“In the Lord” means in the spirit of faith in the Lord, in the order of pleasing Him, and of salvation in Him.
In the Apostle’s words there arises a pleasant consonance. Receive Onesimus, so that you yourself may be useful to me.
Or, so that I too may become Onesimus-like, benefited and gladdened by you.
“Refresh my heart in the Lord.” All our interpreters read: “in Christ.”
Above, in verse 12, the Apostle called Onesimus his heart. But here he speaks of his own heart.
He expresses such strong care for Onesimus that he has no rest and will have none until he sees him again in favorable circumstances.
By this he suggests to Philemon: if you love me, spare me, and care for the peace of my heart, receive him and so refresh my heart.
For without this it cannot be at peace. If you do not wish to do this for my sake, do it for Christ’s sake.
“Show mercy to the Lord, not to me” (St. Chrysostom).
St. Chrysostom interprets “heart” as “my love for you.” Oecumenius repeats the same.
Blessed Theophylact adds to this: “Refresh my love for you, or my heart, for Christ’s sake.”