There is a difference between being a mouthpiece for the Father and speaking for the Father. A mouthpiece repeats exactly what they have been told, in the time and season the Father leads. Whereas speaking for the Father is speaking what one thinks the Father would say whenever they think it should be spoken.
“For I have not spoken of myself; but the Father which sent me, he gave me a commandment, what I should say, and what I should speak. And I know that his commandment is life everlasting: whatsoever I speak therefore, even as the Father said unto me, so I speak” John 12:49-50.