The cause of thirst for life and thirst for rebirth is ignorance of the true self. Real rebirth is dying from the matter(mind) into the Spirit(soul). This is the significance of the crucifixion of Jesus. Whenever identification with the body and the world exists, a body and the world is always available, whether in the duality(dream/waking/vision/astral), till the duality disappears by merging into the Source – the Spirit, or soul (non-duality).
The stone which is projected upwards remains in constant motion, till it returns to its source, the earth, and rests. Pain continues to give trouble, till the pre-pain state is regained.
Quest for self-knowledge or Brahma Gnana or Atma Gnana is inherent in the very nature of life, which is Absolute Existence – truth. Although indestructible by nature, by false identification with its destructible instrument, the body, consciousness imbibes a false apprehension of its destructibility within the false experience of duality; hence it tries to perpetuate that instrument, which results in believing the birth, life and death as reality. But however long these experiences may last; they eventually come to an end and yield to the Self, which alone eternally exists.
Seeker has to give up the false identification with the ‘ego’ which is the false self and, remember, the body and the world cannot exist without the soul, the innermost self, whereas the soul, the innermost self can exist without the body and the world; in fact it is always without it.
People think human being may take an animal birth in some other life. These ideas are based on accepting the present birth as reality. Deeper self-search reveals the fact that, the self is neither the waking entity nor the dream entity but the self is formless soul.. Therefore, from the ultimate standpoint, the present birth, life and death are false hood or illusion. Thus, the seeker has to realize the fact that, the experience birth, life, death and the world are part of the illusion, therefore the rebirth and reincarnation theory is mere imagination based on the false self(waking entity), within the false experience(waking experience).