O {n} my threshing, and the grain of my floor: that which I have heard from the LORD of hosts, the God of Israel, have I declared to you.

(n) Meaning, Babylon.

Wesley's Notes

21:10 Threshing - Threshing is put for the corn threshed; and the corn threshed for people sorely afflicted. This is probably spoken of Babylon. The corn - Which I will cause to be threshed upon the floor. You - Unto you my people; for all the prophecies, even concerning other nations, were published to them, and for their use and comfort.

King James Translators' Notes

corn: Heb. son

Jamieson-Fausset-Brown Bible Commentary

10. my threshing-that is, my people (the Jews) trodden down by Babylon.

corn of my floor-Hebrew, "my son of the floor," that is, my people, treated as corn laid on the floor for threshing; implying, too, that by affliction, a remnant (grain) would be separated from the ungodly (chaff) [Maurer]. Horsley translates, "O thou object of my unremitting prophetic pains." See Isa 28:27, 28. Some, from Jer 51:33, make Babylon the object of the threshing; but Isaiah is plainly addressing his countrymen, as the next words show, not the Babylonians.

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.