John Chrysostom
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.
(ubi sup.) He denounces the haughty and arrogant by the name of mountains, whom Christ has brought low. But by the hills He implies the wreckless, not only because of the pride of their hearts, but because of the barrenness of despair. For the hill produces no fruit.