Charles Ellicott Commentary Isaiah 40:4

"Every valley shall be exalted, and every mountain and hill shall be made low; and the uneven shall be made level, and the rough places a plain:" — Isaiah 40:4 (ASV)

Every valley shall be exalted. — The figure is drawn from the titanic engineering operations of the kingly road-makers of the East, but the parable is hardly veiled. The meek exalted, the proud brought low, wrong ways set right, rough natures smoothed: that is the true preparation for the coming of the Lord, and therefore the true work of every follower of the Baptist in preparing the way. (Luke 3:3–9.)