Our passing through successive incarnations is significant for the overall evolution of our essential being, which has undergone successive past lives and will continue to go through future lives. The evolution of the earth runs parallel to our own. At some point in the future, the earth will have reached the end of its course; then the planet earth, as a physical entity, will have to separate from the totality of human souls — just as when we die the body separates from the spirit, and the soul, in order to live on, enters the spiritual realm between death and rebirth. From this point of view, our highest ideal must be the striving to make all the fruits to be gained in earthly life truly our own before we die.
Source: Rudolf Steiner – GA 15 – The Spiritual Guidance of the Individual and Humanity: Lecture One – Copenhagen, June 6, 1911