A.T. Robertson Commentary Colossians 4:9

"together with Onesimus, the faithful and beloved brother, who is one of you. They shall make known unto you all things that [are done] here." — Colossians 4:9 (ASV)

Together with Onesimus (συν Ονησιμω). Co-bearer of the letter with Tychicus and praised on a par with him, runaway slave though he is.

Who is one of you (ος εστιν εξ υμων). Said not as a reproach to Colossae for having such a man, but as a privilege to the church in Colossae to give a proper welcome to this returning converted slave and to treat him as a brother as Paul argues to Philemon.