John Gill Commentary Luke 3:4

"as it is written in the book of the words of Isaiah the prophet, The voice of one crying in the wilderness, Make ye ready the way of the Lord, Make his paths straight." — Luke 3:4 (ASV)

As it is written in the book of the words of Esaias the prophet (Isaiah 40:3)

saying, the voice of one crying in the wilderness, Prepare you the way of the Lord make his paths straight; (See Gill on Matthew 3:3).