During Jeremiah's time, there were prophets who were speaking lies, not the Word of God.  But God said "The prophet that hath a dream, let him tell a dream; and he that hath my word, let him speak my word faithfully.  What is the chaff to the wheat?"  What are lies and vain words compared to the living and powerful words of God?  We don't need to be intimidated by false doctrines, we just need to be faithful to speak the real Word of God.