From earliest times the belief in the immortality of the “soul” has been widespread, both among primitive societies and the more sophisticated. This issue can be found debated in the Katha UPANISAD, “This doubt that arises, consequent on the death of a man — some saying, ‘It exists,’ and others saying, ‘It does not exist’ — I would know this, under your instruction.” (I.i. 20) PLATO took the view that since the soul exists, its nature must be indestructible and therefore immortality is a fact in Nature.
Theosophical teachings affirms the immortality of the soul because the reincarnating ego or causal body survives death and continues on to a future rebirth. However there are some special cases where this immortality is conditional. Persistent wrong-doing and selfishness can isolate the individual soul (KAMA-MANAS) from “the spark of the divine” or the ATMA (with BUDDHI) and thus immortality is lost. In such a case, the Atma-Buddhi loses its vehicle for action in the world. The detached personality (the “lost” soul) will persist for a while but will eventually disintegrate.