As long as Yaakov remains pre-eminent, the world can reach its fruition, and Esav himself, while being the incarnation of the physical, can also achieve spirituality by supporting Yaakov. Esav, however, wasn't satisfied with his role. He wanted to be the star of the show. He wanted to be the essence of Creation. Esav betrayed his true intentions, to star in Creation, when he asked his father how one tithes salt and straw.
Salt has no intrinsic value.
It finds its value as a condiment to other food. It is always subordinate. Straw, too, is subordinate to wheat. It is the vessel which carries the wheat, its support, its method of existence. But it is not the essence .