“A voice or sound is an obscure utterance, manifesting no secret of the heart but signifying this only: that the one who calls out wants to say something. A word, however, is rational speech, opening the heart’s mystery. While a voice as such is common to both animals and men, a word is fitting only to humans. Thus John was called a voice and not a word, because, through John, God demonstrated neither his mercies nor his justice nor his counsels prepared before the foundation of the world but only this: that God was planning to do something great in human history.”
(Anonymous, Incomplete Work on Matthew, Homily 3)