The salutation of Paul with mine own hand - It is very likely that Paul employed an amanuensis generally, either to write what he dictated, or to make a fair copy of what he wrote. In either case the apostle always subscribed it, and wrote the salutation and benediction with his own hand; and this was what authenticated all his epistles. A measure of this kind would be very necessary if forged epistles were carried about in those times. See the note on 1 Corinthians 16:21, and see Colossians 4:18; (note).
The salutation of Paul with mine own hand; - See the notes, 1 Corinthians 16:21. “Which is the token in every epistle.” Greek: “sign.” That is, this signature is a sign or proof of the genuineness of the epistle; compare the notes on Galatians 6:11.
So I write - Referring, probably, to some mark or method which Paul had of signing his name, which was well known, and which would easily be recognized by them.