As long as Jacob remains pre-eminent, the world can reach its fruition, and Esau himself, while being the incarnation of the physical, can also achieve spirituality by supporting Jacob. Esau, however, wasn t satisfied with his role. He wanted to be the star of the show. He wanted to be the essence of Creation. Esau betrayed his true intentions, to star in Creation, when he asked his father how one tithes salt and straw.
Salt has no intrinsic nutritional value.
It finds its value as a condiment to other foods. 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.