John Wesley on Isaiah 40:6

Cry - God speaks unto his ministers. He - The prophet. All flesh - The prophet having foretold glorious things, confirms the certainty of them, by representing the vast difference between the nature, and word, and work of men and of God. All that men are or have, yea, their highest accomplishments, are but like the grass of the field, weak and vanishing, soon nipt and brought to nothing; but God's word is like himself, immutable and irresistible: and therefore as the mouth of the Lord, and not of man, hath spoken these things, so doubt not but they shall be fulfilled.