Philemon 1:11

"formerly useless to you". For he knows that the acknowledged sin is to extinguish the master's anger. "but now indeed useful both to you and to me". If such faithfulness is useful to Paul, who demands so much, it is clearly also useful to Philemon. …

Therefore, when Onesimus, a fugitive, returned to seek divine assistance, the Apostle baptized him while he was in custody in the city of Rome, seeing the hope of usefulness in him. He commends him in such a way that he indicates his suitability to serve …

Who, although he was once useless to his master (for a slave who steals and runs away harms no one but his own master), now on the contrary, by way of compensation for his usefulness to both his master and Paul, and to others through Paul, he deserves more love than he had previously deserved hatred. He says, "Who was useless to you at one time." "To you alone," he says, "not to others: but now it is useful to both me and you." It is useful to the master in that he could serve Paul as his master; Paul, however, is useful in this: that he could minister to him in the Gospel while he was being held in prison and chains.

All bound slaves who flee to religious communities for refuge should be admonished and sent back to their masters in better dispositions, after the example of St. Paul who, although he had begotten Onesimus through the gospel, sent him back to Philemon. He had convinced Onesimus that the yoke of slavery, borne in a manner pleasing to the Lord, would render him worthy of the kingdom of heaven. Paul not only urged Philemon to annul the threat against his servant, being mindful of the Lord's own words: "If you forgive men their offenses, your heavenly Father will forgive you also your offenses." But also, in order that Philemon might be more kindly disposed toward Onesimus, Paul writes: "For perhaps he therefore departed for a season from you that you might receive him again forever; not as a servant, but instead of a servant, as a most dear brother." If, however, it should be the case of a wicked master who gives unlawful commands and forces the slave to transgress the command of our Master, the Lord Jesus Christ, then it is our duty to oppose him, so that the name of God not be blasphemed by that slave's performing an act displeasing to God.

See how great is his prudence, how he confesses the man's faults, and thereby extinguishes his anger. I know, he says, that he was unprofitable. "But now" he will be "profitable to thee and to me." He has not said he will be useful to thee, lest he should contradict it, but he has introduced his own person, that his hopes may seem worthy of credit, "But now," he says, "profitable to thee and to me." For if he was profitable to Paul, who required so great strictness, much more would he be so to his master.