What if God didn't exist?
"If God does not exist, life is ultimately meaningless. If your life is doomed to end in death, then ultimately it does not matter how you live. In the end it makes no ultimate difference whether you existed or not. Sure, your life might have a relative significance in that you influenced others or affected the course of history. But ultimately mankind is doomed to perish in the heat death of the universe. Ultimately it makes no difference who you are or what you do. Your life is inconsequential."
"Thus, the contributions of the scientist to the advance of human knowledge, the research of the doctor to alleviate pain and suffering, the efforts of the diplomat to secure peace in the world, the sacrifices of good people everywhere to better the lot of the human race—ultimately all these come to nothing. Thus, if atheism is true, life is ultimately meaningless."