Rather, “shall pass beyond his strongholds”; he Shall not stop to take refuge in it through fear (Jdg 20:47; Jer 48:28) [Gesenius].
ensign - the banner of Jehovah protecting the Jews [Maurer].
fire ... furnace - “light” and “fire,” namely, of Jehovah’s altar at Jerusalem (Isa 29:1). Perhaps “furnace,” as distinguished from “fire,” may mean that His dwelling-place (His hearth) was at Jerusalem (compare Isa 4:5); or else the fiery furnace awaiting all the enemies who should attack Jerusalem.