Albert Barnes on Ephesians 6:21

But that ye may know my affairs. May understand my condition, my feelings, and in what I am engaged. To them it could not but be a subject of deep interest,

And how I do. Gr., "What I do;" that is, how I am employed.

Tychicus. Tychicus was of the province of Asia, in Asia Minor, of which Ephesus was the capital. See Acts 20:4. It is not improbable that he was of Ephesus, and that he was well known to the church there. He also carried the letter to the Colossians, Col 4:7, and probably the second epistle to Timothy, 2Ti 4:12. Paul also proposed to send him to Crete to succeed Titus, Tit 3:12. He was high in the confidence of Paul, but it is not known when he was converted, or why he was now at Rome. The Greeks speak of him as one of the seventy disciples, and make him bishop of Colophon, in the province of Asia.

(a) "a beloved brother" Acts 20:4