Moreover; rather, but. The relation of Isaiah 29:5-8 to Isaiah 29:1-4 is that of contrast. The multitude of thy strangers; i.e. "of thy enemies" (comp. Isaiah 25:5). In primitive societies every stranger is an enemy; and hence language—the formation of primitive men—often has one word for the two ideas.
In Latin hostis is said to have originally meant "foreigner" (Cic; 'De Off',' 1.12). Shall be like small dust. Ground down, i.e. to an impalpable powder—rendered utterly weak and powerless. The meaning is determined by the clause which follows, with which it must necessarily be in close accordance.
As chaff that passeth away. "Chaff," in Scripture, is always a metaphor for weakness (comp. Isaiah 5:24; Isaiah 17:13; Isaiah 33:11; Isaiah 41:15; and see also Psalms 1:4; Psalms 35:5; Job 21:18; Hosea 13:3; Daniel 2:35; Zephaniah 2:2).
It has no value; man's object is to get rid of it: a light wind carries it away, and no one inquires whither. Yea, it shall be at an instant suddenly. Dr. Kay says it is "the collapse of Jerusalem" which is here intended.
But most other commentators understand, with more reason, the collapse of her enemies (Cheyne, Delitzsch, Vance Smith, Knobel, etc.).