mountains a way - I will remove all obstructions out of the way (Isa 40:4).
exalted - that is, cast up (Isa 57:14; Isa 62:10); for instance, over valleys. Vitringa explains “mountains” as great kingdoms, Egypt, Syria, etc., subjected to Rome, to facilitate the spreading of the Gospel; “highways,” the Christian doctrine wherein those who join the Church walk, and which, at the time of Constantine, was to be raised into prominence before all, and publicly protected (Isa 35:8, Isa 35:9).