The overall message of this book is that humanity needs to treasure the earth as it's all we've got. Human existence is inexorably tied to earth; it's not possible to live on other worlds, because we are so finely tuned to the earth's biome, which cannot be replicated despite the best and most advanced science. The science in the book is fascinating. The ship AI's contemplation of what is human, good and bad, is thought provoking. The ending will stay with you for days.