"Isaiah was one of the greatest men of all time….In the first place, Isaiah had great natural gifts, which were disciplined and sharpened by the best education that his time afforded. He was blessed with fine judgment and insight, together with the courage to defend to the uttermost a cause he knew to be right. Secondly, he possessed great spiritual intuition and insight, which made him a marvelous and ready instrument in the hands of Jehovah, whom he loved and served with all his heart. Isaiah thus combined earthly and heavenly wisdom to a most unusual degree. All this he of course used for the benefit of his fellow men. Valeton pays this tribute to him: 'Never perhaps has there been another prophet like Isaiah, who stood with his head in the clouds and his feet on the solid earth, with his heart in the things of eternity and with mouth and hand in the things of time, with his spirit in the eternal counsel of God and his body in a very definite moment of history.'"

(As quoted by G. L. Robinson, The Book of Isaiah [First Edition], p. 22.)
(Sidney B. Sperry, The Voice of Israel's Prophets, p. 14.)