Charles Ellicott Commentary Isaiah 29:5

"But the multitude of thy foes shall be like small dust, and the multitude of the terrible ones as chaff that passeth away: yea, it shall be in an instant suddenly." — Isaiah 29:5 (ASV)

Moreover the multitude ... —Better, But. The words interpret those of Isaiah 30:28. The tribulation should be great, but it should last only for a while.

As in Isaiah 25:5, the “strangers”—that is, the “enemies,” and the “terrible ones”—should be brought low. A sudden catastrophe, pointing, probably, to the destruction of Sennacherib’s army, should bring them low. They, too, should pass under the “threshing instrument” of God’s judgments and be as chaff before the wind.