Charles Ellicott Commentary 2 Thessalonians 3:17

"The salutation of me Paul with mine own hand, which is the token in every epistle: so I write." — 2 Thessalonians 3:17 (ASV)

The salutation — At this point, St. Paul takes the pen from his secretary’s hand and adds the closing words himself. The actual salutation does not begin until the benediction of verse 18, to which verse 17 is intended to attract attention.

Which — This refers to the autograph addition of a salutation, or valedictory prayer, not the specific words in which it was expressed.

The token — Rather, a token—a mark by which to distinguish his authentic epistles from the forged letters with which false brothers had troubled the Thessalonian church (2 Thessalonians 2:2). At first sight, it seems too audacious for anyone to have conceived of writing a letter in St. Paul's name. On the other hand, we must remember several points.

1. St. Paul’s genuine First Epistle, despite its claim to inspiration (1 Thessalonians 4:15), could not yet have acquired the sanctity in the eyes of the Thessalonians that it has for us. They had no concept of such a thing as Holy Scripture, and even if they had, St. Paul was a familiar figure—a craftsman who had just left them, not yet invested with a heroic halo.
2. Such literary forgeries were not uncommon in that age and were hardly considered blameworthy unless they were designed to authoritatively teach some heresy. Apocryphal Gospels soon abounded under false titles, and works were attributed to St. Clement and other great Church teachers.
3. There did not always need to be a direct intention to deceive the readers about the authorship. Instead, the renowned name acted as a tempting advertisement for the work, and the theories put forth in this way hit their mark. Whether the real authorship was discovered or not mattered little in comparison.

Such points must be kept in mind before we accept any of the early Christian writings as genuine.

In every epistle — This naturally means, "in every epistle I write." It cannot be narrowly restricted to mean, "in every epistle I will write to you Thessalonians in the future," though that is, of course, its practical significance. Nor does it imply a formal plan to write other epistles to other churches. It seems necessary to suppose that St. Paul had already made it a practice to conclude his letters with his autograph, though only one of his letters is now extant that predates this present epistle.

There is no reason whatever to suppose that all the letters ever written by St. Paul have been preserved for us (see Dr. Lightfoot’s Philippians, page 136 and following), any more than all the sayings and acts of Jesus Christ have been (John 21:25). Even when he wrote his First Epistle to Thessalonica, he had seen the need to give careful directions about his letters (1 Thessalonians 5:27) and to encourage a reasonable skepticism in his correspondents (1 Thessalonians 5:21).

The same concern reappears in 1 Corinthians 16:21 and Galatians 6:11. And, as far as we can tell, St. Paul always observed the rule he had already made. For as Bishop Wordsworth points out regarding 1 Thessalonians 5:28, all his extant epistles contain his "salutation" at the end.

So I write — "This is my handwriting." It does not necessarily mean that the Thessalonians were unacquainted with his handwriting until now; he is only calling their attention to it closely. The large, bold handwriting would not be easily mistaken.