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.
Many people throughout church history have confused the teaching of the apostles that Christ could come at any moment (for believers at the Rapture) and the unbiblical idea that He would come at any moment. The first correct view is the doctrine of imminence, but the second incorrect view involves date setting.