Albert Barnes Commentary Philemon 1:11

"who once was unprofitable to thee, but now is profitable to thee and to me:" — Philemon 1:11 (ASV)

Which in time past was to you unprofitable: either because he was indolent; because he had wronged him ; or because he had run away from him. It is possible that there may be an allusion here to the meaning of the name Onesimus, which denotes profitable (from oninhmi, future onhsw, to be useful, to be profitable, to help); and that Paul means to say that he had until now not well lived up to the meaning of his own name, but that now he would be found to do so.

But now profitable to you. The Greek here is eucrhston, euchreston, but the meaning is about the same as that of the name Onesimus. It denotes very useful. In 2 Timothy 2:21, it is rendered meet for use; in 2 Timothy 4:11 and here, profitable. It does not occur elsewhere in the New Testament.

And to me. Paul had doubtless found him useful as a Christian brother in his bonds, and it is easy to conceive that, in his circumstances, he would greatly desire to keep him with him.