The soul is a concept, not a reality.
To elaborate, the soul is a human-derived concept. It is not a real thing. It is the same type of thing as an idea, as metadata, as fictional stories written to convey complex ethical dilemmas. It is not real in the way that stones, water, air, or electricity are real. It is an intuitive, constructed concept, devised by humankind to describe something essential. It is a single word to describe what something like the saying “the sum is greater than its parts” is getting at.
You have a heart, lungs, a brain, kidneys, bones, muscles… All these things are real, and they are what you are composed of. Yet, looking at ourselves, we “see” that there are essential properties that arise out of the sum of those parts, like personality, that comprise something “more”. There is something about that whole, once all put together, considered all together, in its unique circumstance in this world, that is unique to it, that is essential to it, that is its “essence”. That essence is the soul. Nothing more, nothing less.
I might exemplify it with a sequence of images like this.
First, a circle. An individual unit. Maybe this is one cell in your body, or an individual organ like your heart.
Then, we add some more individual units, say more cells, other organs like your brain, kidneys, digestive tract, muscles, etc.
And as we keep adding, adding some such that they are seen to overlap, then something new as a whole can be perceived to arise. It could be conceived of as no longer just a collection of circles, or even circles in a circle. One could conceive of an overarching image arising, composed from all the individual units. We could call it a “flower”, or something as a whole that is more complex than just a bunch of circles arranged any given way.
This “meta” concept, the “flower”, applied on top of what is really just a collection of circles, arranged in a greater circle, is the “soul”. It is not a “real” thing; it is an abstract concept.
There is no “otherworldly” existence to the thing. It is not a thing that exists on its own outside of your body, outside of “you” existing. It exists because you live. It might change over time as you change. Or perhaps it pertains to aspects of you that are felt or thought to be unchanging and eternally you — for the “you” that existed in this time and place.
For when you die, when you no longer live, it is dead, too. It no longer exists. Or perhaps, in light of this argument, one could say it has now changed into something different — the soul, the essence of a rotting corpse, of decay. But it is not something that keeps on existing, except as imprinted in memory or other marks left in the world by your life. It is not something to fret about beyond your life, or at least not any moreso than you might fret about your legacy, or living a good life and leaving good memories behind, or living a life while you’re alive that is true to yourself. But that is it. That is all.
Beyond that existence in the here and now, in your living flesh and mind and all that is you, beyond that imagining of a flower from circles, there is no such thing. It is not a real thing. Therefore, it is not a valid thing to fret or worry about some “everlasting”, “eternal” soul that will continue on. That “eternal soul” is a concept either of immature, “primitive” humanity trying to arrive at descriptions and understandings of the world and figuring out where the sun goes when it sets each evening. Or it is a conceptual tool with a purpose — to control, to teach, to express the concept of legacy, or many purposes potentially.
Use the concept of the “soul” for what it is. But cease using it as some sort of assertion about an external, greater reality beyond, and cease using it as justification for any action beyond living life according to the most “essential” conception of yourself.