"Affirmation of life is the spiritual act by which man ceases to live thoughtlessly and begins to devote himself to his life with reverence in order to give it true value. To affirm life is to deepen, to make more inward, and to exalt the will to live.Schweitzer, a French-German theologian who won the 1952 Nobel Peace Prize, had many interesting ideas about religion and ethics. While I don't agree with all of his conclusions, he was one of those rare souls who understood that Christianity needed to be modernized, thought long and hard about how to do it, created a new philosophy, and then practiced what he preached.
At the same time the man who has become a thinking being feels a compulsion to give to every will to live the same reverence for life that he gives to his own.[....] This is the absolute, fundamental principle of ethics, and is a fundamental postulate of thought.” - Albert Schweitzer
A compilation of his quotes can be found here.