The Soul is an integral part of all life within the world of Wellspring
Each living creature possesses a collection of Ether that is bonded to their physical forms, wholly unique to each individual, referred to as a Soul. Life cannot exist without a Soul, regardless of the circumstances. A creature with organs perfectly capable of functioning, and likewise healthy in all aspects, but missing a Soul, would not be able to use said organs, rendering it dead.
The Soul is the most basic aspect of an individual, including memories on a subconscious level. Each person is born with a unique soul, which can vary drastically from person to person. This basic soul never changes, each mote of Ether sticking with its owner for the entirety of their life. Souls often grow with their owners, but this is not a necessity. It is perfectly common for individuals to go their whole lives with Souls unchanged from birth.
The primary use of the Soul within Wellspring is as a means of controlling Ether. The Soul provides known ground in Ether, giving its owner an anchor withing the whirling chaos that is the Ether. By leveraging this anchor, individuals can effect change in the Ether, for whatever purpose they desire.
Denizens of Wellspring find utilization of the soul to be as natural as the use of any other part of their bodies. Even infants have been known to move Ether about as they learn control of their bodies. Those with souls control Ether often as simply as if they were controlling intangible limbs.