Adam Clarke on Revelation 6:14

And the heaven departed as a scroll - The whole system of pagan and idolatrous worship, with all its spiritual, secular, and superstitious influence, was blasted, shrivelled up, and rendered null and void, as a parchment scroll when exposed to the action of a strong fire.

And every mountain - All the props, supports, and dependencies of the empire, whether regal allies, tributary kings, dependent colonies, or mercenary troops, were all moved out of their places, so as to stand no longer in the same relation to that empire, and its worship, support, and maintenance, as they formerly did.

And island - The heathen temples, with their precincts and enclosures, cut off from the common people, and into which none could come but the privileged, may be here represented by islands, for the same reasons.