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.

Wesley's Notes

21:6 Go set - This was now done only in a vision, but it signified what should be done really afterwards.

Jamieson-Fausset-Brown Bible Commentary

6. 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 Isa 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."

Matthew Henry's Concise Commentary

21:1-10 Babylon was a flat country, abundantly watered. The destruction of Babylon, so often prophesied of by Isaiah, was typical of the destruction of the great foe of the New Testament church, foretold in the Revelation. To the poor oppressed captives it would be welcome news; to the proud oppressors it would be grievous. Let this check vain mirth and sensual pleasures, that we know not in what heaviness the mirth may end. Here is the alarm given to Babylon, when forced by Cyrus. An ass and a camel seem to be the symbols of the Medes and Persians. Babylon's idols shall be so far from protecting her, that they shall be broken down. True believers are the corn of God's floor; hypocrites are but as chaff and straw, with which the wheat is now mixed, but from which it shall be separated. The corn of God's floor must expect to be threshed by afflictions and persecutions. God's Israel of old was afflicted. Even then God owns it is his still. In all events concerning the church, past, present, and to come, we must look to God, who has power to do any thing for his church, and grace to do every thing that is for her good.