Paul says Onesimus “was indeed useless to you, but now he is useful to you and to me.” He also asks Philemon to receive him as “a beloved brother,” describing a new relational status in the letter’s appeal (Philemon 1:11; Philemon 1:16).
In Philemon 8–11 Paul says he could issue a strong instruction, but instead he chooses to ask. He frames his request “for love’s sake,” presenting himself as an older man and also as someone in prison, which adds weight without forcing the outcome. These verses begin the letter’s main request after Paul has already praised Philemon’s love and the comfort he brings to others (Philemon 4–7). Paul now turns from affirmation to persuasion: he sets up a contrast between what he has the standing to demand and what he chooses to do instead.
Paul presents himself as having real standing “in Christ” to tell Philemon what to do, yet he deliberately chooses not to use that leverage (verse 8). Instead, he frames his approach as an appeal “for love’s sake” (verse 9).
A careful answer keeps the immediate passage, the book's argument, and the whole-Bible storyline together, so the question is answered in context instead of as a detached idea.
Start with Philemon 1:11, then read the surrounding section so the answer stays connected to the passage's flow.
11who once was useless to you, but now is useful to you and to me;