And I will make all my mountains a way - I will make all the mountains for a highway; or an even, level way. That is, he would remove all obstructions from their path. The image is taken from the return from Babylon to the land of Palestine, in which God so often promises to make the hills a plain, and the crooked places straight (see the notes at Isaiah 40:4).
And my highways shall be exalted - That is, the way shall be cast up (see Isaiah 57:14; Isaiah 62:10), as when a road is made over valleys and gulf (see the notes at Isaiah 40:4).