Gregory the Great
Catena Aurea · Johannesevangelium 1
And this is the record of John, when the Jews sent priests and Levites from Jerusalem to ask him, Who art thou? And he confessed, and denied not; but confessed, I am not the Christ. And they asked him, What then? Art thou Elias? And he saith, I am not. Art thou that prophet? And he answered, No. Then said they unto him, Who art thou? that we may give an answer to them that sent us. What sayest thou of thyself? He said, I am the voice of one crying in the wilderness, Make straight the way of the Lord, as said the prophet Esaias. And he said, I am not. Then said they unto him, Who art thou? that we may give an answer to them that sent us. What sayest thou of thyself?
(Hom. vii. c. 2) Ye know that the only-begotten Son is called the Word of the Father. Now we know, in the case of our own utterance, the voice first sounds, and then the word is heard. Thus John declares himself to be the voice, i. e. because he precedes the Word, and, through his ministry, the Word of the Father is heard by man.