As for John Baptist, he professeth himself to be no more than a voice. And so indeed he was totus vox, all voice.
His apparel, his diet, his conversation did preach holiness as well as his doctrine,
#Mr 6:20: For Herod feared John, knowing that he was a just man and an holy, and observed him; and when he heard him, he did many things, and heard him gladly.
See also John 3:25-36. (Comm. on Mark 1:1)
The painting: Herri met de Bles – Landscape with Saint John the Baptist Preaching