Without spiritual development there is no real useful evolution in this world. We can evolve in a scientific way or on the material level of existence but if we deny the spirit, we are not going to be able to use these developments in a proper way.  Spirituality is essential to every human being as much as oxygen is to plants and flowers. If you want to know why, just ask your self this question. If there is nothing more to life but materialistic and mental pursuits, does that make me happy and fulfilled? Most of us will find this answer to be a no. True happiness comes from developing something deeper within our selves. Some spiritual traditions call this the seeking of salvation,  ascension, liberation or enlightenment.