4 And that we may not have to ask, Of what God was the Word made flesh? He does himself previously teach us, saying, “There was a man sent from God, whose name was John. The same came as a witness, that he might bear witness of that Light. He was not that Light, but [came] that he might testify of the Light.” By what God, then, was John, the forerunner, who testifies of the Light, sent [into the world]? Truly it was by Him, of whom Gabriel is the angel, who also announced the glad tidings of his birth: [that God] who also had promised by the prophets that He would send His messenger before the face of His Son, who should prepare His way, that is, that he should bear witness of that Light in the spirit and power of Elias. But, again, of what God was Elias the servant and the prophet?
Of Him who made heaven and earth, as he does himself confess. John, therefore, having been sent by the founder and maker of this world, how could he testify of that Light, which came down from things unspeakable and invisible? For all the heretics have decided that the Demiurge was ignorant of that Power above him, whose witness and herald John is found to be. Wherefore the Lord said that He deemed him “more than a prophet.” For all the other prophets preached the advent of the paternal Light, and desired to be worthy of seeing Him whom they preached; but John did both announce [the advent] beforehand, in a like manner as did the others, and actually saw Him when He came, and pointed Him out, and persuaded many to believe in Him, so that he did himself hold the place of both prophet and apostle.
For this is to be more than a prophet, because, “first apostles, secondarily prophets;” but all things from one and the same God Himself.
Source: Adversus haereses (New Advent)