In my opinion, the most important book would be Euclid's Elements. It's had a far more lasting contribution to the advancement of the human race than any religious book, be it Bible, Qu'ran, or Guru Granth Sahib.
It was one of the first books to show systematic proofs and sets the foundation of mathematics today. Pretty much all mathematicians have read it, whereas I doubt most Christians have read the Bible.
It was one of the first books to show systematic proofs and sets the foundation of mathematics today. Pretty much all mathematicians have read it, whereas I doubt most Christians have read the Bible.