The voice said, Cry. — Literally, A voice saith, Cry. The questioner (“and one said”) is probably the prophet himself, asking what he is to proclaim. The truth which he is to enforce thus solemnly is the ever-recurring contrast between the transitoriness of man and the eternity of God and of His word, taking that term in its highest and widest sense. Two points of interest may be noted: (1) that this is another parallelism with Job (Job 14:2); (2) the naturalness of the thought in one who, like Isaiah, was looking back, as Moses looked (Psalms 90:5-6) in extreme old age upon the generations whom he had survived, and forward to the fall of mighty monarchies one after another. The marginal references show how dominant the thought is in the mind of Isaiah. Isaiah himself had uttered it in Isaiah 2:22.
Related Commentaries of Isaiah 40:6
Isaiah 40:6
6 The voice said, Cry. And he said, What shall I cry? All flesh is grass, and all the goodliness thereof is as the flower of the field: