The shape it assumes is the determination of its own substance. Essence is not something extrinsic to existence which limits and determines it in the way that a pitcher shapes its recipient liquid, but essence is rather the place where existence stops. There is nothing in water which is not water. There is nothing in an existent which is not existence. Essence is the intrinsic limitation of esse , the crystallization of existence, bordered by nothingness.
Essence gives to being that it is of a certain type or kind.
Esse gives to essence its existence. Essence is not a positive being apart from the existence of which it is the limitation, but it is definitely a positive principle of philosophy when understood as the intrinsic limitation of esse . Its function can be designated by affirmative terms, contraction, refraction, channeling of perfection, specification, determination. All essences are modes of esse . The created essence is not its esse , it is the intrinsic limitation of esse , the prism through which the intelligible riches and perfections of esse are refracted and contracted to this kind of being.