Is the soul immortal? In that it surpasses human mortality and steadily grows, learning and increasing in mass and wisdom with each incarnation - it is immortal. But what is mortality for a soul? It is born, in a manner of speaking, on 3rd Density worlds where it forms within creatures intelligent enough to offer the spark. Forming entities react to their surroundings, and as the stuff of souls is everywhere in the Universe, forming takes place to some degree in many living things but dissipates for lack of a spark. Like pollen that cannot grow unless moved by an external agent, a bee or the winds, forming entities in moss or bugs or tall trees or birds is a potential only, and dissipates when the life form dies.
Worlds are seeded with life and later seeded with intelligent life, a genetically engineered variation of a native species, so as to give forming entities a leg up. Intelligence is the spark that causes forming entities to build to the point where they do not dissipate, as they themselves have become alive. We have mentioned that souls do not die during nuclear explosions, nor do they lose themselves in Black Holes. Entities are of material that can affect its surroundings while remaining untouched. The stuff of souls does not feed, nor does it expend itself. It influences its surroundings by manipulation of its surroundings, like a puppet master pulling strings, rather than expending its resources like an audience throwing tomatoes. Souls, once formed, do not die. They may grow rapidly or slowly, may stagnate or plateau for a long time or forever, but they do not die, nor do they shrink. Beyond this, we cannot say, as we ourselves know no more.