Accordingly, though I am bold enough in Christ to command you to do what is required,
Διὸ πολλὴν ἐν Χριστῷ παρρησίαν ἔχων ἐπιτάσσειν σοι τὸ ἀνῆκον
Ver. 8. Wherefore, though I might be much bold in Christ to enjoin you that which is convenient [befitting].
Observe how cautious he is, lest any of the things which were spoken even from exceeding love should so strike the hearer, as that he should be hurt. For this reason before he says, to enjoin you, since it was offensive, although, as spoken out of love, it was more proper to soothe him, yet nevertheless from an excess of delicacy, he as it were corrects it by saying, Having confidence, by which he implies that Philemon was a great man, that is You have given confidence to us. And not only that, but adding the expression in Christ, by which he shows that it was not that he was more illustrious in the world, not that he was more powerful, but it was on account of his faith in Christ — then he also adds, to enjoin you, and not that only, but that which is convenient, that is, a reasonable action. And see out of how many things he brings proof for this. You do good to others, he says, and to me, and for Christ's sake, and that the thing is reasonable, and that love gives.
[For moral, see Phm 1:16]
Haydock Catholic Bible Commentary: Philemon
Wherefore, though I might have much confidence, &c. Now S. Paul disposeth Philemon to grant his request, I am persuaded I might command thee, and thou wouldst not take it amiss. Wi. — To command thee, &c. As an apostle of Jesus Christ, I have the power even of ordering thee to forgive Onesimus, and to receive him again into favour; likewise as Paul, the aged, respect and regard being always due in a particular manner to old men; or again, as a prisoner of Jesus Christ, suffering here out of love for Jesus Christ and the faithful: I might here make use of all these different reasons to induce thee to pardon a poor fugitive slave, but I will not; I merely as a poor humble supplicant, forgetting all the dignity due to my apostleship, my grey hairs, or my chains, beseech thee to pardon him. Nor can I for a moment doubt of obtaining my request, when I consider the great charity thou hast in Jesus Christ towards all the saints. Calmet. A.