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.
(20. in Ev.) Or, the valley when filled increases, but the mountains and hills when brought low decrease, because the Gentiles by faith in Christ receive fulness of grace, but the Jews by their sin of treachery have lost that wherein they boasted. For the humble receive a gift because the hearts of the proud they keep afar off.