not to be easily disconcerted or alarmed by any spirit or message or letter seeming to be from us, alleging that the Day of the Lord has already come.
KJV
That ye be not soon shaken in mind, or be troubled, neither by spirit, nor by word, nor by letter as from us, as that the day of Christ is at hand.
ASV
to the end that ye be not quickly shaken from your mind, nor yet be troubled, either by spirit, or by word, or by epistle as from us, as that the day of the Lord is just at hand;