By means of their altars, incense stands and dungy idols, the unfaithful Israelites were polluting the mountains, hills, valleys and banks of the stream beds of their God-given possession.

Actually, their polluted condition all hinged on their bad attitude toward Jehovah. So the only way to cleanse the land was to take drastic action against its defilers, so that those mountains, stream beds and valleys would be clean and the land would, in effect, ‘know that God is Jehovah.’