Charles Ellicott Commentary Isaiah 40:5

"and the glory of Jehovah shall be revealed, and all flesh shall see it together; for the mouth of Jehovah hath spoken it." — Isaiah 40:5 (ASV)

The glory of the Lord shall be revealed. — Did the prophet think of a vision of a glory-cloud, like the Shechinah which he had seen in the Temple? Or had he risen to the thought of the glory of character and will, of holiness and love? (John 1:14)

All flesh. — The revelation is not for Israel only, but for mankind. So in Luke 3:6, the words are quoted from the Septuagint, all flesh shall see the salvation of God. The phrase meets us here for the first time, and occurs again in Isaiah 49:26; Isaiah 66:16; Isaiah 66:23–24, marking, so to speak, the growing catholicity of the prophet’s thoughts. (See Note on Isaiah 38:11)