not to be quickly shaken in your mind, nor yet be troubled, either by spirit, or by word, or by letter as from us, saying that the day of Christ had come.
neither by spirit: "Spirit" is from pneuma, which means "one in whom a spirit is manifest or embodied; hence i.e. actuated by a spirit, whether divine or demoniacal; one who either is truly moved by God’s Spirit or falsely boasts that he is" (Thayer 522-2-4151) (see also 1 John 4:1-3 and 1 Timothy 4:1). Paul is teaching "if someone teaches something different from what we have taught, do not believe them." Paul teaches the same message saying: