God wants both our body (our physical being) and our soul (our inner being) to be kept clean and holy, which is why He forbids not just impure outward actions, looks and talk, but also thoughts and desires we entertain in the heart and mind. To deal properly with lust (as with any impurity), there is something fundamental that must be present in our hearts before we will kill the hold sins have upon us: Having a transformative understanding of Sin and its consequences.