*Minor differences ignored. Grouped by changes, with first version listed as example.
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.
Go, set a watchman - This was said to Isaiah in the vision. He represents himself as in Babylon, and as hearing God command him to set a watchman on the watch-tower who would announce what was to come to pass. All this is designed merely to bring the manner of the destruction of the city more vividly before the eye.
For thus hath the (i) Lord said to me, Go, set a watchman, let him declare what he seeth.
(i) That is, in a vision by the spirit of prophecy.
For thus hath the Lord said unto me,.... This is a confirmation of the above prophecy from the Lord himself, he showing to the prophet, in a visionary way, the ruin of Babylon, and the means and instruments of it:
go, set a watchman; not Habakkuk, as Jarchi; nor Urias, as the Septuagint; nor Jeremiah, as others; but himself, who, in a way of vision, represented a watchman on the walls of Babylon; and which was no way unsuitable to his character and office as a prophet:
let him declare what he seeth; what he sees coming at a distance, or at hand, let him faithfully and publicly make it known: these are not the words of the king of Babylon to one of his watchmen; but of the Lord of hosts to his prophet.
Go, set a watchman, let him declare what he seeth--God's direction to Isaiah to set a watchman to "declare" what he sees. But as in Isaiah 21:10, Isaiah himself is represented as the one who "declared." HORSLEY makes him the "watchman," and translates, "Come, let him who standeth on the watchtower report what he seeth."
The prophecy is continued with the conjunction "for" (ci). The tacit link in the train of thought is this: they act thus in Babylon, because the destruction of Babylon is determined. The form in which this thought is embodied is the following: the prophet receives instruction in the vision to set a metzappeh upon the watch-tower, who was to look out and see what more took place. "For thus said the Lord to me, Go, set a spy; what he seeth, let him declare." In other cases it is the prophet himself who stands upon the watch-tower (Isaiah 21:11; Habakkuk 2:1-2); but here in the vision a distinction is made between the prophet and the person whom he stations upon the watch-tower (specula). The prophet divides himself, as it were, into two persons (compare Isaiah 18:4 for the introduction; and for the expression "go," Isaiah 20:2). He now sees through the medium of a spy, just as Zechariah sees by means of the angel speaking in him; with this difference, however, that here the spy is the instrument employed by the prophet, whereas there the prophet is the instrument employed by the angel.
Go set - This was now done only in a vision, but it signified what should be done really afterwards.
*More commentary available at chapter level.