If birth, life and death are illusion then all conducts actions and their fruits are mere illusion

 As Sri, Sankara says:  When the whole universe, movable and immovable, is known to be Atman, and thus the existence of everything else is negated, where is then any room to say that the body is Atman.

 If waking entity  is not the self then the karma theory has no meaning because the ultimate truth is based on the soul or Atman, the innermost self.  . Thus no second thing exists other than Atman ,which is present in the form of consciousness, therefore why to view the worldview on the standpoint of the waking entity as self (ego)  when the waking entity  or ego is the false self, and the soul or Atman is the true self.

 If body is not the self, then the birth, life, death and the universe are bound to be illusion.  If birth, life and death are illusion then all conducts actions and their fruits are mere illusion. If body is not the self, then the existence of god, heaven and hell is mere illusion.  If body is not the self then all religious beliefs of god is mere illusion.  If body is not the self but the Atman [soul] which is in the form of consciousness is the true self, then there is no scope for second thing other than consciousness, therefore consciousness, which is Atman is Brahman or ultimate truth.  The Brahman alone is real and eternal.  Thus whatever is real eternal has to be identified as god. To identify the real and eternal, one has to overcome the ignorance caused by the illusion. To overcome the ignorance one has to acquire the Self-Knowledge or Brahma Gnana or Atma Gnana.