Gregory the Great
Catena Aurea · Lukasevangelium 3
And he came into all the country about Jordan, preaching the baptism of repentance for the remission of sins; As it is written in the book of the words of Esaias the prophet, saying, The voice of one crying in the wilderness, Prepare ye the way of the Lord, make his paths straight. Every valley shall be filled, and every mountain and hill shall be brought low; and the crooked shall be made straight, and the rough ways shall be made smooth; And all flesh shall see the salvation of God.
(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.