Albert Barnes Commentary Isaiah 30:25

"And there shall be upon every lofty mountain, and upon every high hill, brooks [and] streams of waters, in the day of the great slaughter, when the towers fall." — Isaiah 30:25 (ASV)

In the day of the great slaughter — When the enemies of God's people will have been destroyed—probably in a time after the slaughter of the Assyrian army.

When the towers fall — The towers of the enemy; perhaps referring here to the towers of Babylon. After they had fallen, the Jews would be favored with the time of prosperity to which the prophet here refers.