Assimilating spiritual thoughts on Earth is fundamental to achieving consciousness after death  

The ideas of ancient religious founders gave something to human souls that awakened them spiritually and gave them strength to perceive in the etheric world, and that also means to lead a conscious life after death. Assimilating modern spiritual science will in turn give our soul the strength to develop the necessary power of thinking after death to consciously perceive its etheric environment. Both people of ancient times who followed their religious founders and modern people who are willing to understand spiritual science will be able to find their way after death.

Only one type of person will have difficulty in finding his or her way after death. In fact, this type will frequently not even experience a life after death, because it will have become so dulled and obscured. This sort of person is the dyed-in-the-wool materialist who clings to images of the physical world and does not want to develop any strength to perceive the world we enter after death. In terms of the soul-spiritual, to be a materialist really means the same as wanting to destroy one’s eyes and ears in the physical world, gradually deadening one’s senses. It is no different from someone saying, “These eyes — they can’t be trusted, they provide only impressions of light. Away with them! These ears — they perceive only vibrations, not the one single truth. Get rid of them! Get rid of the senses, one by one!” To be a materialist in regard to the spiritual world makes as much sense as this attitude in regard to the sensory world. 

Source: Rudolf Steiner – GA 154 – THE PRESENCE OF THE DEAD on the Spiritual Path: LECTURE ONE: UNDERSTANDING THE SPIRITUAL WORLD (PART ONE) – Berlin, April 18, 1914