The concept of the immortal soul is one that is incredibly difficult to defend in reason and observation, difficult to connect to one’s body, and hard to differentiate from an ethereal mind. Instead, it’s much easier to promote just the mind, as the mind is something we phenomenally experience as well as have a physical counterpart to.
The mind is a metaphysical entity, a center of operations, that is a byproduct of a field effect emanating from the human body. As the whole is not the sum of its parts, the field effect of the mind cannot be wholly observed through human brain composition or activity.
An analogy of this would be software visuals on a computer. The image created from a data file cannot be observed in the binary code alone, but as a composite visual product created on the display. Our thoughts manifest themselves, not in the physical material that is the composition of our brains, but in our actions. A similar analogy may also be made with that of the relationship between subatomic particles and physical objects. The subatomic particles alone share little in common with the qualities of a physical object, but the composition of all of the subatomic objects in a certain arrangement creates a perceivably unique object.
Under this notion of the mind, the relationship with the body becomes evident. The failing of our bodies, whether due to illness, age, or death, weakens or entirely eliminates the field effect. Additionally, anything that occurs to our body will have some degree of repercussion upon the field effect that is our mind. Because of this relationship, when we die our mind does not live on like a soul is believed to do, but instead the mind ceases to exist as the whole system of the body fails.
This makes our immortality less of an individual one, and rather manifested in our contributions to the world and other people in whatever form our talents allow.