Isaiah 42:15

I will make waste mountains and hills, and dry up all their herbs; and I will make the rivers islands, and I will dry up the pools.

I will make waste mountains - I will destroy all my proud and elated foes.

Mountains - namely, the enemies' mountains, clad with vines and olives on the terraced sides: an image of the prosperous enemy.

I will make the rivers islands - dry lands. God will destroy His foes, the pagan, and their idols, and 'dry up' the fountains of their oracles, their doctrines and institutions, the symbol of which is water, and their schools which promoted idolatry (Vitringa).