6. For thus hath the Lord said to me. The Prophet is commanded to set a watchman on the watchtower, to see these things at a distance; for they cannot be perceived by the eyes, or learned by conjecture. In order, therefore, that all may know that he did not speak at random, he declares that he foretells these things; for although they are unknown to men, and incredible, yet he clearly and distinctly knows them by the spirit of prophecy, because he is elevated above the judgment of men. This ought to be carefully observed; for we must not imagine that the prophets learned from men, or foresaw by their own sagacity, those things which they made known; and on this account also they were justly called “Seers.” (1 Samuel 9:9.) Though we also see them, yet our sight is dull, and we scarcely perceive what is at our feet; and even the most acute men are often in darkness, because they understand nothing but what they can gather by the use of reason. But the prophets speak by the Spirit of God, as from heaven. The amount of what is stated is, that whosoever shall attempt to measure this prophecy by their own judgment will do wrong, because it has proceeded from God, and therefore it goes far beyond our sense.
Go, appoint a watchman. It gives additional weight that he “appoints a watchman in the name of God.” If it be objected, “You relate incredible things as if they had actually happened,” he replies that he does not declare them at random; for he whom the prince has appointed to be a watchman, sees from a distance what others do not know. Thus Isaiah saw by the revelation of the Spirit what was unknown to others.