shall ... shall - rather, “God rebuketh (Psa 9:5) them, and they flee - are chased”; the event is set before the eyes as actually present, not future.
chaff of ... mountains - Threshing floors in the East are in the open air on elevated places, so as to catch the wind which separates the chaff from the wheat (Psa 88:13; Hos 13:3).