The soul is the breath of life in the sense that without the soul the body could not function.
You are right that this could be a long discussion and it is late here so I will leave you with a couple of things I have posted that describe what I believe the soul is and what happens to our body and soul when we die. Then we can pick this discussion up later if you want to.
The soul comes into being at the moment of conception and it animates the human body. The body needs a soul or it cannot live, but the soul does not need a body, so it continues to exist after the body dies. The body is destructible and temporary so eventually it dies; the soul is indestructible and eternal so it lives forever in the spiritual world.
Let me try to explain what I meant about the soul’s functions as briefly as possible. The soul (spirit) cannot be perceived in the material world, except as it is expressed in outward signs and works. The human body is visible, the soul is invisible. Nevertheless, it is the soul that directs human faculties. As outer circumstances are communicated to the soul by the eyes, ears, and brain, the soul communicates its desires through the brain to the physical body, which thereby expresses itself.
The soul is the sum total of the personality so it is the person himself; the physical body is pure matter with no real identity. The person, after he dies and leaves his physical body behind remains the same person, and he goes to the spiritual world where he continues the life he conducted in the physical world. The soul takes on some kind of a spiritual form made up of elements that exist in the spiritual world. Nobody can understand what that will be like before they die because the only reference point we have is the physical world and the physical body.
I believe the physical body dies only once and it remains dead in forever. When the physical body dies, the spirit (soul) leaves the body and passes from one world into another.
421. When the body is no longer able to perform the bodily functions in the natural world that correspond to the spirit’s thoughts and affections, which the spirit has from the spiritual world, man is said to die. This takes place when the respiration of the lungs and the beatings of the heart cease. But the man does not die; he is merely separated from the bodily part that was of use to him in the world, while the man himself continues to live. It is said that the man himself continues to live since
man is not a man because of his body but because of his spirit, for it is the spirit that thinks in man, and thought with affection is what constitutes man. Evidently, then, the death of man is merely his passing from one world into another. And this is why in the Word in its internal sense “death” signifies resurrection and continuation of life.
Heaven and Hell, p. 351
I call that other world the spiritual world, but there is no real separation, as the spiritual world is within this world.
“Those who have passed on through death, have a sphere of their own. It is not removed from ours; their work, the work of the Kingdom, is ours; but it is sanctified from what we call ‘time and place.’ Time with us is measured by the sun. When there is no more sunrise, and no more sunset, that kind of time does not exist for man. Those who have ascended have different attributes from those who are still on earth, yet there is no real separation.” ‘Abdu’l-Bahá in London, pp. 95-96
After the soul takes its flight to the spiritual world, the soul continues to progress on its journey through the spiritual world where it will endure forever.
“And now concerning thy question regarding the soul of man and its survival after death. Know thou of a truth that the soul, after its separation from the body, will continue to progress until it attaineth the presence of God, in a state and condition which neither the revolution of ages and centuries, nor the changes and chances of this world, can alter. It will endure as long as the Kingdom of God, His sovereignty, His dominion and power will endure. It will manifest the signs of God and His attributes, and will reveal His loving kindness and bounty.” Gleanings From the Writings of Bahá’u’lláh, pp. 155-156