You grive for those who are not worthy of grief and yet you speak words of wisdom, the wise grive neither for living nor for the dead.
People meet and depart in this world as two pieces of wood, flowing down the river, came together and the separate from each other. the wise who knows that the body is mortal and Atma is immortal has nothing to moan about (Katha Upanishad 2.22).
Atma mean consciousness , Brahma, Spirit soul,self sources of life and cosmic power behind the body-mind complex.
just as our body in exists Atma, the space of consciousness.
Atma cannot be perceived by our senses, because Atma is beyond the domain of the senses, senses can only comprehend physical things.