The salutation, with my own hand. Here again he provides against the danger, of which he had previously made mention -- lest epistles falsely ascribed to him should find their way into the Churches. For this was an old artifice of Satan -- to put forward spurious writings, that he might detract from the credit of those that are genuine; and farther, under pretended designations of the Apostles, to disseminate wicked errors with the view of corrupting sound doctrine. By a singular kindness on the part of God, it has been brought about that, his frauds being defeated, the doctrine of Christ has come down to us sound and entire through the ministry of Paul and others. The concluding prayer explains in what manner God aids his believing people -- by the presence of Christ's grace.

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.

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).

(16) The salutation of Paul with mine own hand, which is the token in every epistle: so I write.
(16) The apostle writes the conclusion of his letter with his own hand, so that false letters might not be brought and put in place of true ones.

The salutation of Paul with mine own hand,.... In writing his epistles, the body and substance of them he used an amanuensis, but the salutation he wrote with his own hand:
which is the token in every epistle; by which they might be known to be true and genuine, and be distinguished from counterfeit ones: and the rather he mentions this, that they might be troubled neither by word, nor by spirit, nor by epistle, as from them, as they had been, 2-Thessalonians 2:2 for it seems that this wicked practice of counterfeiting the epistles of the apostles, or carrying about spurious ones, under their name, began so early; to prevent which, the apostle took this method,
so I write, as follows:

The Epistle was written by an amanuensis (perhaps Silas or Timothy), and only the closing salutation written by Paul's "own hand" (compare Romans 16:22; 1-Corinthians 16:21; Colossians 4:18). Wherever Paul does not subjoin this autograph salutation, we may presume he wrote the whole Epistle himself (Galatians 6:11).
which--which autograph salutation.
the token--to distinguish genuine Epistles from spurious ones put forth in my name (2-Thessalonians 2:2).
in every epistle--Some think he signed his name to every Epistle with his own hand; but as there is no trace of this in any manuscripts of all the Epistles, it is more likely that he alludes to his writing with his own hand in closing every Epistle, even in those Epistles (Romans, Second Corinthians, Ephesians, Philippians, First Thessalonians) wherein he does not specify his having done so.
so I write--so I sign my name: this is a specimen of my handwriting, by which to distinguish my geniune letters from forgeries.

The salutation of Paul. Here he adds the salutation in his own hand-writing. The Epistle thus far had been written by one to whom he dictated, as was his custom, but he now adds his autograph. This autograph was proof of the genuineness. Their attention is perhaps called to this on account of a spurious epistle (2-Thessalonians 2:2).