A.T. Robertson 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)

Of me Paul with mine own hand (τη εμη χειρ Παυλου). Instrumental case χειρ. Note genitive Παυλου in apposition with possessive idea in the possessive pronoun εμη. Paul had dictated the letter, but now wrote the salutation in his hand.

The token in every epistle (σημειον εν παση επιστολη). Mark (verse 14) and proof of the genuineness of each epistle, Paul's signature. Already there were spurious forgeries (2 Thessalonians 2:2). Thus each church was enabled to know that Paul wrote the letter. If only the autograph copy could be found!