Gregory the Great — as excerpted in the Catena Aurea on Luke 3:3-6

“(7, 20. in Ev.) John cries in the desert because he brings the glad tidings of redemption to deserted and forsaken Judæa, but what he cries is explained in the words, Prepare ye the way of the Lord. For they who preach true faith and good works, what else do they than prepare the way for the Lord’s coming into the hearts of the hearers, that they might make the paths of God straight, forming pure thoughts in the mind by the word of good preaching.”