" Be for Man the memory of Earth and Origin. Remember this Earth. Never forget her, but — never come back. If you come back, you might meet the Archangel at the east end of Earth, guarding her passes with a sword of flame. I feel it. Space is your home hereafter. It’s a lonelier desert than ours. God bless you, and pray for us. "

― Walter M. Miller Jr. , A Canticle for Leibowitz (St. Leibowitz, #1)