Jamieson, Fausset and Brown on Isaiah 49:11

11. my--All things are God's.

mountains a way--I will remove all obstructions out of the way (Is 40:4).

exalted--that is, cast up (Is 57:14; 62:10); for instance, over valleys. Vitringa explains "mountains" as great kingdoms, Egypt, Syria, &c., 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 (Is 35:8, 9).