1 Luke also, the follower and disciple of the apostles, referring to Zacharias and Elisabeth, from whom, according to promise, John was born, says: “And they were both righteous before God, walking in all the commandments and ordinances of the Lord blameless.” And again, speaking of Zacharias: “And it came to pass, that while he executed the priest's office before God in the order of his course, according to the custom of the priest's office, his lot was to burn incense;” and he came to sacrifice, “entering into the temple of the Lord.” Whose angel Gabriel, also, who stands prominently in the presence of the Lord, simply, absolutely, and decidedly confessed in his own person as God and Lord, Him who had chosen Jerusalem, and had instituted the sacerdotal office.
For he knew of none other above Him; since, if he had been in possession of the knowledge of any other more perfect God and Lord besides Him, he surely would never— as I have already shown — have confessed Him, whom he knew to be the fruit of a defect, as absolutely and altogether God and Lord. And then, speaking of John, he thus says: “For he shall be great in the sight of the Lord, and many of the children of Israel shall he turn to the Lord their God. And he shall go before Him in the spirit and power of Elias, to make ready a people prepared for the Lord.” For whom, then, did he prepare the people, and in the sight of what Lord was he made great?
Truly of Him who said that John had something even “more than a prophet,” and that “among those born of women none is greater than John the Baptist;” who did also make the people ready for the Lord's advent, warning his fellow-servants, and preaching to them repentance, that they might receive remission from the Lord when He should be present, having been converted to Him, from whom they had been alienated because of sins and transgressions. As also David says, “The alienated are sinners from the womb: they go astray as soon as they are born.” And it was on account of this that he, turning them to their Lord, prepared, in the spirit and power of Elias, a perfect people for the Lord.
Source: Adversus haereses (New Advent)