Jamieson, Fausset and Brown on Isaiah 30:17

17. One thousand--A thousand at once, or, "As one man" [Maurer].

rebuke--the battle cry.

shall ye--at the rebuke of five shall ye, namely, all (in contrast to the "one thousand") flee so utterly that even two shall not be left together, but each one shall be as solitary "as a signal staff" [G. V. Smith], or "a banner on a hill" (Is 5:26; 11:12). The signal staff was erected to rally a nation in war. The remnant of Jews left would be beacons to warn all men of the justice of God, and the truth of His threatenings. Gesenius (from Le 26:8; De 32:30) arbitrarily inserts "ten thousand." "At the rebuke of five shall ten thousand of you flee."