He was once useless to me, but is now useful to [both] you and me. [Note: Since the name Onesimus means "useful," it appears Paul is making an intentional play on the word].

not as a slave [only], but more than a slave, as a dearly loved brother. [He is that] to me especially, but how much more to you, both in a physical way [i.e., by continuing to serve as your slave] and in [the fellowship of] the Lord [i.e., now also as your brother in Christ].