Consider a stone. A stone exists within the world but the stone does not "have" a world. What is the difference? Having a world means existing within a field of relations in connection with some interior power. The dirt does not have a world. A plant within the dirt, though, does. The dirt, inasmuch as it provides the plant with nutrients, nutrients which are "taken into" the plant in both a literal and a figurative fashion, is part of the world of the plant. The plant has a relatedness to the dirt in the way a stone does not.
Is there a simpler distinction that can be made between things that "have" worlds and things that are merely within worlds? Of course. What else are we describing other than the difference between living and non-living things? To be a living thing is to have a soul, and the soul is the interior power by which living things possess fields of relations.
Not all living things contain within themselves identical fields of relations, though. Animals have more expansive fields of relations than plants, and human beings' fields of relations are even more expansive than irrational animals. By considering the degree to which living things have fields of relations, then, we can establish a hierarchy of being and existence.
But what is man's proper field of relations? Being in its totality! As a being that is capable of knowing, man is able to place himself in relation to all things simply. What do we call this activity of placing oneself in relation to Being as a whole?